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Foot and Disorders Capturing Moti on With Ultrasound: Blood, Muscle, Needle, and

Photo by Michael D. Stubblefi eld, MD and Ankle Nerve Disorders

Tracy A. Park, MD David R. Del Toro, MD Atul T. Patel, MD, MHSA Jeffrey A. Mann, MD

AANEM 58th Annual Meeting San Francisco, California

Copyright © September 2011 American Association of Neuromuscular & Electrodiagnostic Medicine 2621 Superior Drive NW Rochester, MN 55901

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2 Foot and Ankle Nerve Disorders

Table of Contents

Course Objectives & Course Committee 4

Faculty 5

Tarsal Tunnel Syndromes 7 Tracy A. Park, MD

First Branch Lateral Plantar Neuropathy: “Baxter’s Neuropathy” 17 David R. Del Toro, MD

Foot Related to Peroneal (Fibular) Nerve Entrapments (Deep and Superficial) and Digital Neuromas 25 Atul T. Patel, MD

Surgical Management of Entrapment Neuropathies in the Foot, Including Indications and Outcomes 33 Jeffrey A. Mann, MD

CME Questions 51

Dr. Mann is a consultant and speaker for Small Bone Innovations. Any conflict of interest was resolved according to ACCME standards. All other authors/faculty have nothing to disclose.

Course Chair: Benjamin S. Warfel, MD

The ideas and opinions expressed in this publication are solely those of the specific authors and do not necessarily represent those of the AANEM.

3 Objectives

Objectives - Participants will acquire skills to (1) discuss the anatomy of the foot as it relates to entrapment of, and electrodiagnostic study of, the terminal branches of the , deep peroneal nerve, and superficial peroneal nerve, (2) discuss the clinical presentation and differential diagnosis of syndrome, Baxter’s nerve entrapment (i.e., 1st branch lateral plantar neuropathy), “anterior tarsal tunnel” syndrome (i.e., deep peroneal nerve entrapment), superficial peroneal nerve entrapment, Joplin’s neuroma and Morton’s neuroma, (3) devise and perform an electrodiagnostic examination that effectively addresses suspected focal nerve entrapments in the foot, and (4) discuss the surgical and nonsurgical management of focal nerve entrapments in the foot, including indications and outcomes. Target Audience: • Neurologists, physical medicine and rehabilitation and other physicians interested in neuromuscular and electrodiagnostic medicine • Health care professionals involved in the management of patients with neuromuscular diseases • Researchers who are actively involved in the neuromuscular and/or electrodiagnostic research Accreditation Statement - The AANEM is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education (CME) for physicians. CME Credit - The AANEM designates this live activity for a maximum of 3.25 AMA PRA Category 1 CreditsTM. If purchased, the AANEM designates this enduring material for a maximum of 6.75 AMA PRA Category 1 CreditsTM. This educational event is approved as an Accredited Group Learning Activity under Section 1 of the Framework of Continuing Professional Development (CPD) options for the Maintenance of Certification Program of the Royal College of Physicians and Surgeons of Canada. Physicians should claim only the credit commensurate with the extent of their participation in the activity. CME for this course is available 09/2011 - 09/2014. CEUs Credit - The AANEM has designated this live activity for a maximum of 3.25 AANEM CEUs. If purchased, the AANEM designates this enduring material for a maximum of 6.75 CEUs.

2010-2011 Course Committee

Shawn J. Bird, MD, Chair Taylor B. Harrison, MD A. Arturo Leis, MD Philadelphia, PA Atlanta, GA Jackson, MS

Gary L. Branch, DO Laurence J. Kinsella, MD Marcy C. Schlinger, DO Owosso, MI Saint Louis, MO Okemos, MI

Lawrence W. Frank, MD Shashi B. Kumar, MD Benjamin S. Warfel, MD Elmhurst, IL Tacoma, WA Lancaster, PA

2010-2011 AANEM President

Timothy R. Dillingham, MD, MS Milwaukee, Wisconsin

4 Foot and Ankle Nerve Disorders

Faculty David R. Del Toro, MD Tracy A. Park, MD Associate Professor Physiatrist Department of Physical Medicine and Rehabilitation Aurora Medical Group Medical College of Wisconsin Clinical Faculty Milwaukee, Wisconsin Department of Physical Medicine & Rehabilitation Medical College of Wisconsin Dr. Del Toro is currently an associate professor in the Department Milwaukee, Wisconsin of Physical Medicine and Rehabilitation at the Medical College of Wisconsin and is presently on staff at Froedtert Hospital in Dr. Park is currently in private practice with the Aurora Medical Milwaukee. In addition to electrodiagnostic medicine, his clinical Group in Milwaukee. In addition, he serves as volunteer faculty practice includes amputee/prosthetic rehabilitation along with for the Department of Physical Medicine and Rehabilitation at being the medical director for the comprehensive acute inpatient the Medical College of Wisconsin. He completed his residency rehabilitation program at Froedtert Hospital. He earned his in physical medicine and rehabilitation residency at the medical degree at Indiana University School of Medicine and Rehabilitation Institute of Chicago and went on to complete a performed an internship in general surgery at Methodist Hospital fellowship in electrodiagnostic medicine at the Medical College of of Indiana in Indianapolis. He then completed a residency in Wisconsin under the tutelage of Dr. Jacqueline Wertsch. Dr. Park physical medicine and rehabilitation at the Medical College of is board-certified by the American Board of Electrodiagnostic Wisconsin. Dr. Del Toro is board-certified by the American Board Medicine (ABEM), the American Board of Physical Medicine of Electrodiagnostic Medicine (ABEM) and American Board of and Rehabilitation, and the National Board of Medical Examiners. Physical Medicine and Rehabilitation. He is a member of several He is an active member of the American Academy of Physical professional societies, including the American Association of Medicine and Rehabilitation and the Association of Academic Neuromuscular & Electrodiagnostic Medicine (AANEM) and Physiatrists. As an active member of the American Association the American Academy of Physical Medicine and Rehabilitation. of Neuromuscular & Electrodiagnostic Medicine (AANEM), he Dr. Del Toro has served on several committees for the AANEM, has served on the Education Committee and the Tarsal Tunnel including Practice Issues Review Panel, Syndrome Task Force and has been an oral examiner for the Task Force, and the Workshop Committee and he is presently an ABEM for many years. He is a regularly invited speaker at the active member of the Marketing Committee. He has been an oral AANEM annual scientific meetings. He has also served asa examiner for the ABEM. Also, he is currently a manuscript reviewer manuscript reviewer for the Archives of Physical Medicine and for the Archives of Physical Medicine and Rehabilitation. Rehabilitation.

Jeffrey A. Mann, MD Atul T. Patel, MD, MHSA Department of Physiatrist Division of Neuromuscular Diseases Kansas City Bone & Joint Clinic, PA University of Washington Medical Center Overland Park, Kansas Seattle, Washington Dr. Patel earned a bachelor of science in chemical engineering at Dr. Jeffrey Mann is in private practice Orthopedic Surgery in the University of Houston before entering medical school at Baylor Oakland, California. His practice focuses on sports medicine College of Medicine. He then studied rehabilitation medicine and degenerative conditions of the foot and ankle. Dr. Mann has at the University of Washington and later became Residency authored book chapters and scientific papers about numerous Program Director for the Department of Rehabilitation Medicine topics, including ankle replacements, ankle arthroscopy and at the University of Kansas Medical Center. He is currently a cartilage repair techniques, bunion repair, and ankle ligament physiatrist at the Kansas City Bone & Joint Clinic in Kansas City. injuries. Dr. Mann is a team physician for the University of He also serves as the Medical Director of the adult program at the California at Berkeley. 5 Rehabilitation Institute of Kansas City. Dr. Patel is board-certified by the American Board of Physical Medicine and Rehabilitation (ABPMR), the ABPMR subspecialty of spinal cord injury medicine, the American Board of Independent Medical Examiners, and the American Board of Electrodiagnostic Medicine (ABEM). He is a member of several professional organizations, including the American Academy of Physical Medicine and Rehabilitation, the American Paraplegia Society, the American Institute of Ultrasound Medicine, and the American College of Healthcare Executives. He is also active in the AANEM and has served on several committees and on the board. He is an oral examiner for the ABEM. Dr. Patel also is a reviewer for the journals Stroke, Archives of Physical Medicine and Rehabilitation, and the American Journal of Physical Medicine & Rehabilitation.

6 Tarsal Tunnel Syndromes

Tracy A. Park, MD Physiatrist Aurora Medical Group Clinical Faculty Department of Physical Medicine & Rehabilitation Medical College of Wisconsin Milwaukee, Wisconsin

INTRODUCTION affected branch was the inferior calcaneal nerve (ICN) (also called “Baxter’s nerve”), which had electrical abnormalities in 17% of Tarsal tunnel syndrome (TTS) is the most common entrapment feet. neuropathy of the tibial nerve.52 It can be described as a constellation of signs and symptoms caused by compression ANATOMY of the tibial nerve in the region deep to the flexor retinaculum. The clinical features of TTS were first described in 1918 by von The boundaries of the anatomic tarsal tunnel are as follows: the Malaise,37 and a posttraumatic mechanism was first proposed roof is formed by the flexor retinaculum (laciniate ligament); in 1933 by Pollack and Davis based on anatomic dissections.46 the floor is formed by the medial surface of the talus, the However, the first published case reports appeared in 1962, when sustentaculum tali, and the medial surface of the ; the Keck32 and Lam,35 in separate articles, presented single cases of proximal border is formed by the superficial and deep aponeurotic tibial nerve compression at the ankle; both authors proposed the of the leg; the distal border is formed by the plantar aspect term “tarsal tunnel syndrome” for the condition. of the navicular; and the inferior border is formed by the abductor hallucis (AH).44,52 Despite a large body of literature regarding TTS, it remains a controversial topic in many respects. Along with providing Unlike the dense, tough carpal ligament, the flexor retinaculum a description of the anatomic, clinical, and electrodiagnostic is a thin, flimsy structure with ill-defined borders. Often, itis (EDX) features of TTS, this discussion will address some of those difficult, or impossible, to identify where the aponeurotic fascia controversies. of the leg ends and the flexor retinaculum begins.45

INCIDENCE At the level of the talus, the tarsal tunnel may be divided into the proximal (tibiotalar) tarsal tunnel and the distal (talocalcaneal) Although TTS is relatively uncommon—incidence rates of 0.5% tarsal tunnel.44 In the proximal tarsal tunnel, the deep surface of and 0.6% have been reported52—it is probably underdiagnosed. the flexor retinaculum sends multiple distinct fibrous septae down As Saeed pointed out in 2004,52 the “exact incidence . . . does to the periosteum of the calcaneus. These septae divide the tarsal depend on how hard someone looks for it.” In a recent retrospective tunnel into individual smaller tunnels that contain the tibial nerve, study59 of 272 consecutive patients seen in a specialized foot the and vein, and the tendons of the tibialis (EMG) clinic, 27% were found to have posterior, flexor digitorum longus, and flexor hallucis longus isolated neuropathies of at least one branch of the tibial nerve muscles.52 in the foot, including 5% with classic TTS. The most commonly 7 TARSAL TUNNEL SYNDROMES

Figure 1. Medial aspect of a right foot. Note that Baxter’s nerve, usually the 1st branch off the LPN, in this case, branches off the tibial nerve, but still eventually lies deep to the AH. Also, the MCN branches pierce the FR as they course towards the medial/plantar aspect of the heel. (Adapted from Park T. and Del Toro D. Electrodiagnostic evaluation of the foot. Phys Med Rehabil Clin North Amer 1998;9:871-896, with Figure 2. Cutaneous innervation of the plantar aspect of the foot. permission.) (Adapted from Sarrafian SK. Anatomy of the foot and ankle. Philadelphia: JB Lippincott Co; 1983, with permission.) AH = ; FR = flexor retinaculum; IFS = interfascicular septum; LPN = lateral ; MCN = medial calcaneal nerve; MPN 1 = medial calcaneal nerve; 2 = lateral calcaneal nerve; 3 = saphenous = ; QP = quadratus plantae muscle; TN = tibial nerve. nerve; 4 = ; 5 = medial plantar nerve; 6 = .

The distal tarsal tunnel is divided by the interfascicular septum different from those of the MPN and LPN.3,4,42,47,55 (IFS), a dense, relatively thick extension of the deep fascia of the AH that attaches to the medial calcaneus to split the distal The MCN usually is the first of the four branches to come off the tarsal tunnel into the upper and lower calcaneal chambers (Fig. tibial nerve. It is a purely sensory nerve that provides cutaneous 1). The upper chamber carries the medial plantar nerve (MPN) innervation to the posterior, medial, and plantar aspects of the heel and the lower chamber carries the lateral plantar nerve (LPN). (Fig. 2). Although it usually originates as a separate branch, it can The medial and and vein course with their also arise from the LPN or from the MPN/LPN bifurcation.45 The respective through the chambers.17,29,40,44 After exiting MCN travels a short way within the proximal tarsal tunnel before the calcaneal chambers, the MPN and LPN pass through their piercing the flexor retinaculum to course toward the heel. respective abductor canals, narrow openings between the medial calcaneonavicular ligament and the attachment of the AH to the The ICN usually is the next branch to arise from the tibial nerve. It navicular.43,44,48 was first named and described by Roegholdt in 1940.50 (It is known more commonly in the surgical world as “Baxter’s nerve,” but it NEUROANATOMY is mostly referred to in the EDX literature as “the first branch of the LPN” or “the nerve to the abductor digiti minimi.”) The ICN The tibial nerve provides cutaneous innervation to the of arises directly from the tibial nerve about half the time, and as a the foot, and it also innervates all of the intrinsic muscles except proximal branch of the LPN the other half.53 At the entrance to the the extensor digitorum brevis (EDB). In over 90% of feet, the distal tarsal tunnel, the ICN veers inferiorly to pass between the tibial nerve bifurcates into the MPN and LPN within the upper deep fascia of the AH medially and the quadratus plantae laterally. tarsal tunnel.15,28 Contrary to the classical anatomic concept of the It then takes a sharp turn laterally across the foot, coursing just structures in the tarsal tunnel, the tibial nerve should be thought anterior to the tuberosity of the calcaneus. Along the way, it of as having four terminal branches (Fig. 1): the MPN, the LPN, supplies sensation to the anterior calcaneal periosteum. It always the ICN, and the medial calcaneal nerve (MCN).44 The thinking provides motor innervation to the abductor digiti quinti pedis behind this model is that the ICN—the most commonly entrapped (ADQP), and it often supplies the quadratus plantae and flexor distal tibial nerve branch59—sometimes arises as a separate branch digitorum brevis.44 The ICN provides no cutaneous innervation of the tibial nerve5,27,44 and has entrapment sites that are completely to the foot. 8 FOOT AND ANKLE NERVE DISORDERS The MPN and LPN are the final two branches of the tibial nerve, these case reports fail to document response amplitudes or the splitting in the upper tarsal tunnel before entering the upper and needle EMG examination, aspects of testing that could show the lower calcaneal chambers, respectively. presence of axonal degeneration.

The MPN innervates the AH, flexor hallucis brevis, flexor On the axonal degeneration side are the case reports in which digitorum brevis, and first lumbrical. It also provides cutaneous needle EMG demonstrates evidence of denervation in the tibial- innervation to the medial sole and the plantar surfaces of the first, innervated intrinsic muscles of the affected feet.34,54 There is also second, third, and medial half of the fourth (Fig. 2). a report of patient who underwent resection of his distal tibial nerve for intractable pain due to TTS. The histopathologic reading The LPN innervates the quadratus plantae, flexor digiti minimi noted striking axonal degeneration, but made no mention of brevis, flexor hallucis brevis, AH, all the interossei, and the second, demyelination.39 third, and fourth lumbricals. It provides cutaneous innervation to the lateral sole, as well as to the plantar aspect of the fifth and It is the author’s experience that a vast majority of TTS cases are lateral half of the fourth (Fig. 2). diagnosed based on axonal degeneration, and that most of these cases show no evidence of the slowed conduction across the tarsal ETIOLOGY tunnel that would be expected with demyelination.

TTS may occur in either the proximal or distal tarsal tunnel.29,49 CLINICAL FEATURES Proximal TTS results from compression of the tibial nerve proper in the retromalleolar region, and tends to produce symptoms History attributable to dysfunction of all (or most) of the terminal tibial nerve branches. Distal TTS results from entrapment of the MPN, Typically, patients with TTS present because of burning or aching LPN, or both, at sites along the course of these nerves, including pain in the sole of the foot that tends to be worse at night.44 The the interfascicular septum and the abductor canals. Although pain also may be reported as tingling, cramping, and tightness. It entrapment of the ICN usually is lumped into the “distal TTS” is often poorly localized, and may spread proximally up the leg. category, it is not technically a distal TTS, because the potential Numbness in the sole of the foot also is a common complaint, sites of compression of the ICN (i.e., its sharp turn around the but the medial heel is typically spared since the MCN origin is so quadratus plantae, and its course across the anterior calcaneus) proximal. Symptoms tend to worsen with prolonged weightbearing. are not part of the anatomic distal tarsal tunnel. Distal TTS spares Patients may complain of a feeling of instability in the affected the MCN, since it exits the proximal tarsal tunnel by piercing the foot and ankle during the stance phase, but complaints of actual flexor retinaculum. weakness are rare.

The causes of TTS have been divided into five broad Physical Examination categories17,26: Patients with TTS often have a Tinel’s sign over the tibial nerve in • Trauma and post-traumatic changes: The most common the region of the tarsal tunnel. However, because of the possibility cause of TTS.36 Includes cumulative microtrauma, foot and of entrapment of the individual branches in the distal tarsal tunnel, ankle fractures, ankle sprains, and surgical procedures on percussion should be extended distally into this region. In some the foot and ankle. patients, percussion sends a painful sensation proximally (Valleix • Compression by space-occupying lesions: Includes phenomenon). Palpation also may reveal tenderness over the tibial anomalous/hypertrophied muscles, ganglia, schwannoma, nerve in the tarsal tunnel. Forceful passive ankle eversion and/ neurilemoma, tenosynovitis, and chronic thrombophlebitis. or great toe extension may reproduce the pain and paresthesias. • Systemic causes: Includes diabetes mellitus, hyperlipidemia, Weakness of the intrinsic foot muscles is extremely difficult to gout, hypothyroidism, acromegaly, , and detect because selective activation of these muscles is virtually varicosities. impossible for most people. However, some patients may display • Biomechanical causes related to joint structure: Includes visible atrophy of the tibial-innervated intrinsic muscles. There tarsal joint impaction due to hypermobility of the first ray, may also be a detectable sensory deficit in the distribution of rigid joint structures, tarsal joint coalition, and rearfoot one or more of the tibial nerve branches; this is best tested with varus. pinprick, because of the calluses on most people’s soles.44 • Idiopathic. ELECTRODIAGNOSTIC STUDIES PATHOPHYSIOLOGY Nerve Conduction Studies The actual pathophysiologic mechanism of TTS is a point of considerable controversy. Is it demyelination or axonal Because of the possibility of isolated focal entrapment of the degeneration? individual tibial nerve branches, nerve conduction studies (NCSs) should be performed on the MPN, LPN, and ICN. If heel pain is Arguing in favor of a demyelinating process are case reports a major component of the patient’s clinical presentation, then the that diagnose TTS based on prolonged distal motor or sensory MCN also should be tested. latencies in the MPN and/or LPN.2,34,54 Unfortunately, many of 9 TARSAL TUNNEL SYNDROMES Motor

There are several published techniques for motor NCSs on the MPN, LPN and ICN.38 The compound muscle action potentials (CMAPs) obtained may be abnormally small or delayed in TTS.14 Stimulation for all three branches is behind the medial , 8 cm proximal to the E1 recoding site for the MPN. The MPN is recorded with the E1 over the AH, just posterior and inferior to the navicular tuberosity (Fig. 3A).31 The electrode should be placed as close to the navicular tuberosity as possible, since placement more than 1 cm away can lead to spuriously-prolonged latencies caused by false motor points.12 Although two techniques have been proposed for recording the LPN CMAP (Fig. 3C)—one placing E1 proximal in the foot31 and the other placing it more distal30—anatomical dissections10 have shown that only the distal one assesses the LPN, but that it does so by recording the CMAP of the flexor digiti minimi brevis, which is always innervated by the LPN. The more proximal technique (Fig. 3B) actually assesses the ICN by recording the ADQP, which is always innervated by this nerve.

Techniques also have been proposed for determining tibial motor conduction across the tarsal tunnel.20,25 These methods record CMAPs for the MPN and LPN while stimulating proximal to, and distal to, the flexor retinaculum (Fig. 4). A problem with these techniques is that the distal stimulation site may remove the contribution of the ICN-innervated muscles from the recorded CMAP, and it is unclear what effect this change might have on the resulting latency and amplitude in any given foot. Recently published techniques2,56 that use intramuscular recording of CMAPs show promise in helping diagnose neurapraxic lesions in the plantar nerves.

Sensory

Agreement is fairly universal that sensory (or mixed) NCSs of the plantar nerves are more sensitive than motor NCSs at detecting abnormalities of the plantar nerves.17 The sensory NCSs are Figure 3. Recording sites for MPN, ICN (Baxter’s nerve), and LPN recorded either orthodromically or antidromically, using either CMAPs. surface electrodes or near-nerve needle electrodes to record ADMP = abductor digiti minimi pedis; CMAP = compound muscle action over the appropriate nerve (Fig. 5).13,38 A segmental technique potential; FDMB = flexor digiti minimi brevis; ICN = inferior calcaneal nerve; measuring conduction across the tarsal tunnel also has been LPN = lateral plantar nerve; MPN = medial plantar nerve. proposed.7 Orthodromic sensory NCSs of the MPN and LPN stimulate the first and fifth toes, respectively, while recording over the tibial nerve above the flexor retinaculum. Antidromic studies reverse these simulating and recording sites. The acquired sensory nerve action potentials (SNAPs) from both techniques are very small, even when extensive signal averaging is employed, which makes these studies very time-consuming. Furthermore, in addition to the unpleasantness of the many stimuli that are needed for signal averaging, the near-nerve technique has the added pain of the needle insertion and placement. And despite all the time and discomfort that may be required, adequate SNAPs are difficult to obtain, even in normal, healthy individuals.

Mixed

Figure 4. Felsenthal’s method A mixed NCS technique can be utilized for the MPN and LPN, and it eliminates many of the drawbacks of the sensory NCS techniques (Fig. 6).51 This technique applies stimuli to the sole 10 FOOT AND ANKLE NERVE DISORDERS

Figure 5. Sensory of the plantar nerves.

over the MPN and LPN while recording 14 cm proximally over the tibial nerve behind the medial malleolus. Recording is all performed with surface electrodes. The technique is relatively quick and well tolerated. The mixed nerve action potentials (NAPs)—predominantly generated by the sensory fibers—are much larger than the MPN and LPN SNAPs, and they are less frequently absent (although thick , edema, calluses, and advanced age can result in unobtainable responses52). One study showed MPN mixed NAPs to be comparable in amplitude to Figure 6. Mixed nerve conduction study of the plantar nerves. the sural SNAP, with the LPN mixed NAPs somewhat smaller.11 Another study found that the mixed NCS was less sensitive, but more specific, than the sensory NCS for detecting TTS.23 Because of the decreased likelihood of false-positive studies, the authors of that study recommended the mixed NCS over the sensory NCS.

An antidromic MCN sensory NCS technique (Fig. 7) can be performed by placing E1 at a site one-third of the way from the tip of the heel to a point midway between the navicular tuberosity and the medial malleolar prominence.45 Stimulation is over the tibial nerve at the ankle 10 cm proximal to the E1 electrode on the medial heel, with E2 at the apex of the heel. All electrodes are surface electrodes. It is important to realize that, because the entire tibial nerve is stimulated, a recorded CMAP is unavoidable;45 it has at a longer latency than the MCN SNAP, giving the sensory Figure 7. Sensory Nerve Conduction Study of the medial calcaneal potential an appearance that resembles the median pre-motor nerve potential in the .

Needle Electromyography activity in the feet of 50 normal, healthy subjects; they found it in only a single intrinsic muscle in only one of the feet they Needle EMG of the intrinsic foot muscles is possibly the most tested.16 underutilized tool available to EDX physicians, largely because of several widespread misconceptions regarding the test. Second, many EDX physicians believe that needle EMG of the foot is prohibitively painful. Again, this has not been found to be First, there is the notion that needle EMG abnormalities are true in the author’s laboratory. When performed correctly, it is common in normal intrinsic foot muscles, a notion based on no more painful than needle EMG of the intrinsic hand muscles, several studies that showed prolonged insertional activity in which are tested routinely in most laboratories. up to 20% of intrinsic foot muscles tested. None of the studies found fibrillation potentials or positive sharp waves in any of the Third, because the first two reasons prevent EDX physicians feet tested.19,24,58 In the author’s laboratory, prolonged insertional from attempting needle EMG of the intrinsic foot muscles, many activity in normal feet is a rare finding, and there is almost never believe they are on shaky ground when it comes to interpreting abnormal spontaneous activity. A more recent study by Dumitru whatever it is that they observe. and colleagues looked specifically at true abnormal spontaneous 11 TARSAL TUNNEL SYNDROMES

Table 1. Differential diagnosis of tarsal tunnel syndrome

There are several options for intrinsic foot muscles that can be needled without undo pain in order to evaluate all three motor branches of the tibial nerve. In the author’s laboratory (Table 1), the AH (Fig. 8) is tested for the MPN (flexor hallucis brevis is another option), the fourth dorsal interosseus pedis (Fig. 9) is tested for the LPN (flexor digiti minimi brevis is another option), and the ADQP (Fig. 10) is tested for the ICN.* When testing of a nontibial-innervated intrinsic foot muscle is desired, the only A option is the EDB, innervated by the lateral (“motor”) branch of the deep peroneal nerve (Fig. 11).

Needle EMG of the intrinsic muscles is a critical part of the EDX evaluation of the foot. Needle EMG abnormalities are the most frequent “positive” finding in patients with TTS in the author’s laboratory.

ENTRAPMENT OF INDIVIDUAL TIBIAL NERVE B BRANCHES IN THE FOOT

Figure 8A and 8B: Needle electrode placement for needle EMG Entrapment of individual tibial nerve branches in the foot account examination of abductor hallucis (AH). The needle electrode is inserted for a majority of “tibial” neuropathies in the foot, far surpassing about 2 cm posterior to the navicular tuberosity, at (or immediately superior TTS in frequency, according to a recent study.59 to) the junction of the dorsal and plantar skin (the needle tip piercing the thinner dorsal skin). The electrode shaft can be directed posteriorly at Entrapment of the Medial Plantar Nerve and/ about a 45-degree angle (A), or slightly distally (B). When advancing the or Lateral Plantar Nerve by the Interfascicular needle electrode, one must be cognizant of the medial and lateral plantar Septum nerves which are nearby but deep to the AH. The MPN and/or LPN may be entrapped at the proximal or distal edge of the IFS,17 compressed by increased pressure within the nondistensible calcaneal chambers themselves,29 or injured by traction. The patient’s symptoms usually consist of sensory complaints in the distribution of the MPN, LPN, or both. There also may be vague pain in the medial foot. Physical examination may show tenderness and a Tinel’s sign at the entrance or exit of the lower tarsal tunnel, or along its entire length. A sensory

*Although the first dorsal interosseus pedis—classically innervated by Figure 9. Needle electrode placement for needle EMG examination the LPN—is a good muscle to include when testing for a peripheral of fourth dorsal interosseus pedis (fourth DIP). The needle electrode is (since it is very distal and relatively well-tolerated), it inserted into the fourth dorsal web space immediately proximal to the should not be used when testing for focal neuropathies of the tibial nerve fourth and fifth metatarsal heads. The needle electrode is angled toward branches. According to an anatomic study,1 the first dorsal interosseus the heel to direct it into the space between the metatarsal shafts. pedis is dually innervated by the LPN and the medial branch of the deep peroneal nerve in 92.1% of feet; by contrast, the fourth dorsal interosseus pedis seems to be purely innervated by the LPN. So for the cleanest possible study of an LPN-innervated muscle, the fourth dorsal interosseus pedi—or alternatively the flexor digiti minimi brevis—is used. 12 FOOT AND ANKLE NERVE DISORDERS deficit may be found in the distribution of the affected plantar nerve. NCSs may show abnormal motor, sensory, or mixed nerve responses in the MPN or LPN, with no abnormalities in any of the other NCSs in the foot or in the contralateral plantar nerve. Needle EMG is abnormal in the distribution of the affected plantar nerve only.

Entrapment of the Medial Plantar Nerve and/ or Lateral Plantar Nerve by the Abductor Canal: Jogger’s Foot Figure 10. Needle electrode placement for needle EMG examination of There are reports of entrapment of either or both plantar nerves abductor digiti quinti pedis (ADQP). The needle electrode tip is inserted in the abductor canals.43,48 The proposed mechanism is AH at (or immediately superior to) the junction of the dorsal and plantar hypertrophy or prolonged running with a valgus running style skin (so the tip pierces the thinner dorsal skin) and approximately 1 to 2 (“jogger’s foot”).48 Patients typically report burning or paresthesias fingerbreadths proximal to the base of the fifth metatarsal (see markin in the distribution of the affected plantar nerve(s).41,43,48 Physical figure). The electrode shaft should be directed posteriorly at about a 45- examination may show tenderness and/or a Tinel’s sign just degree angle, an orientation that will guide it into the bulk of the ADQP proximal to the navicular tuberosity,41,43,48 as well as a plantar muscle belly. sensory deficit. Inspection may show forefoot valgus.41 NCSs41,43,48 and needle EMG43 show a constellation of findings similar to those seen with entrapment by the IFS.

Entrapment of the Inferior Calcaneal Nerve (“Baxter’s nerve”)

Entrapment of the inferior calcaneal nerve is by far the most common distal tibial nerve entrapment59 and will be covered in a separate, dedicated lecture. A Medial Calcaneal Neuropathy

This small, purely sensory nerve can be entrapped as it passes through the tight, dense fascia overlying the medial calcaneus,55 affected by chronic external injury (shoe-wear or repeated heel- strike against a hard surface),6,8 or it can be irritated by excessive forefoot pronation.8 Patients complain of pain or paresthesias over the medial heel, worse with weightbearing.6 Physical examination may show tenderness and/or a Tinel’s sign somewhere along the course of the MCN, possibly with a Valleix phenomenon. A sensory deficit may be found over the medial heel, as well as tingling on sensory testing. Long-standing MCN insult can lead to pseudoneuroma formation similar to a Morton’s “neuroma,”8 and a sudden electric shock-like discomfort can be elicited when an extremely tender, engorged MCN pseudo-neuroma is rolled B by palpation (“lamp-cord sign”).6,8,9 EDX testing shows only an abnormal MCN sensory study. Figure 11. Needle electrode placement for needle EMG examination of ELECTRODIAGNOSTIC APPROACH extensor digitorum brevis (EDB). The needle electrode tip is inserted into the lateral edge of the EDB at the midpoint of the muscle belly (A). If there The differential diagnosis for TTS (Table 2) should be kept in is little or no palpable EDB muscle mass, the needle electrode is inserted mind when performing an EDX consultation to evaluate for about 2 cm posterior and 2 cm superior to the base of the fifth metatarsal. this condition. In addition, because entrapment of individual The bellies of the EDB lie lateral to and deep to the tendons of the extensor tibial nerve branches in the foot is even more common than TTS digitorum longus. An attempt should be made to explore all four muscle itself,59 and because the symptoms of nerve entrapments in the bellies by directing the needle electrode in a very shallow angle medially foot tend to be vague and only somewhat helpful, it is imperative across the foot (B), thereby allowing the needle to pass just deep to the when assessing a patient for TTS that testing be performed on long extensor tendons. multiple motor and sensory branches of the tibial nerve. Motor and sensory/mixed nerve conduction studies (NCSs) as well as needle EMG can assist in confirming the diagnosis of TTS in over 90% of cases.52 13 TARSAL TUNNEL SYNDROMES

Table 2. Differential diagnosis of tarsal tunnel syndrome REFERENCES 1. Proximal or “true” tarsal tunnel syndrome (TTS) 2. Medial plantar neuropathy in the distal tarsal tunnel or 1. Akita K, Sakamoto H, Sato T. Lateromedial and dorsoplantar abductor canal borders among supplying areas of the nerves innervating the 3. Lateral plantar neuropathy in the distal tarsal tunnel or intrinsic muscles of the foot. Anat Rec 1999;255:465-470. abductor 2. Almeida DF, Scremin L, Zuniga SF, Oh SJ. Focal conduction block 4. canal in a case of tarsal tunnel syndrome. Muscle Nerve 2010;42:452- 5. Chronic compressive medial and/or lateral plantar 455. neuropathy 3. Arenson DJ, Cosentino GL, Suran SM. The inferior calcaneal 6. Medial calcaneal neuropathy nerve: an anatomical study. J Amer Podiatry Assoc 1990;70:552- 7. Baxter’s neuropathy (or inferior calcaneal neuropathy) 560. 8. Generalized 4. Baxter DE, Pfeffer GB. Treatment of chronic heel pain by surgical 9. Distal tibial neuropathy secondary to, or TTS release of the first branch of the lateral plantar nerve. Clin Orthop complicated by, Rel Res 1992;279:229-236. 10. generalized peripheral neuropathy 5. Baxter DE, Thigpen M. Heel pain. Operative results. Foot Ankle 11. Proximal tibial neuropathy 1984;5:16-25. 12. Sciatic neuropathy, lumbosacral , or 6. Cohen SJ. Another consideration for the diagnosis of heel pain: neuroma of the medial calcaneal nerve. J Foot Surg 1974;13:128. 13. Musculo-ligamentous: , soft tissue 7. David WS, Doyle JJ. Segmental near-nerve sensory conduction sprains/strains, tenosynovitis, and bursitis studies of the medial and lateral plantar nerves. Electromyogr Clin Neurophysiol 1996;36:411-417. 8. Davidson MR, Copoloff JA. Neuromas of the heel. Clin Pod Med Surg 1990;7:271-288. 9. Davidson MR. Heel neuroma: identification and removal. J Am In a patient with suspected TTS, the standard EDX evaluation in Podiatr Assoc 1977;67:431-435. the affected foot should include: (1) motor NCSs of the MPN, LPN, 10. Del Toro DR, Mazur A, Dwzierzynski WW, Park TA. and ICN; (2) mixed or sensory NCSs of the MPN and LPN (and, Electrophysiologic mapping and cadaveric dissection of the lateral if appropriate, the MCN); (3) needle EMG of muscles supplied foot: Implications for tibial motor nerve conduction studies. Arch by the MPN (using the AH, or possibly the flexor hallucis brevis), Phys Med Rehabil 1998;79:823-826. LPN (using the fourth dorsal interosseus pedis, or possibly the 11. Del Toro DR, Park TA, Vennix MJ, Wertsch JJ. Medial calcaneal flexor digiti minimi brevis), and ICN (using the ADMP) (Table 1); nerve, medial plantar nerve and sural nerve comparison. Muscle and (4) needle EMG of muscles proximal to the foot (including Nerve 1993;16:1114. at least one muscle supplied by the tibial nerve) to screen for a 12. Del Toro DR, Park TA. Abductor hallucis false motor points: sciatic neuropathy or a lumbosacral radiculopathy or plexopathy electrophysiologic mapping and cadaveric dissection. Muscle (possibly including tibial H waves, if deemed appropriate). Nerve 1996;19:1138-1143. 13. DeLisa JA, Lee HJ, Baran EM, Lai K, Spielholz N, Mackenzie K. If NCS abnormalities are found, the possibility of a peripheral Manual of nerve conduction velocity and clinical neurophysiology, polyneuropathy must be considered. Therefore, additional 3rd ed. New York: Raven Press; 1994. NCSs should be performed on nerves other than the tibial nerve, 14. DeLisa JA, Saeed MA. AAEE case report #8: The tarsal tunnel including other sensory nerves (sural or superficial peroneal) syndrome. Muscle Nerve 1983;6;664-670. or motor nerves (deep peroneal), as appropriate, and possibly 15. Dellon AL, Mackinnon SE. Tibial nerve branching in tarsal tunnel. expanded to the contralateral foot. Arch Neurol 1984;41:645-646. 16. Dumitru D, Diaz CA, King JC. Prevalence of denervation in If needle EMG abnormalities are seen in any tibial-innervated paraspinal and intrinsic foot musculature. Am J Phys Med Rehabil muscles, those muscles should be tested in the contralateral foot 2001;80:482-490. in order to clearly establish that the abnormalities are not due to a 17. Dumitru D, Amato AA, Zwarts MJ. Electrodiagnostic medicine, more generalized process. In addition, the EDB should be needled 2nd ed. Philadelphia: Hanley & Belfus; 2002. as well, in order to test a muscle outside the tibial nerve supply. 18. Erickson SJ, Quinn SF, Kneeland JB, Smith JW, Johnson JE, Carrera GF, Shereff MJ, Hyde JS, Jesmanowicz A. MR imaging of Other than EDX testing, additional studies to consider include the tarsal tunnel and related spaces: normal and abnormal findings plain radiographs (to identify bony abnormalities, such as with anatomic correlation. AJR Am J Roentgenol 1990;55:323- fractures, exostoses, and accessory ossicles), weightbearing 328. radiographs (to help demonstrate any deformities), and magnetic 19. Falck B, Alaranta H. Fibrillation potentials, positive sharp waves resonance imaging scans (to evaluate the nonbony contents of and fasciculation in the intrinsic muscles of the foot in healthy the tarsal tunnel18,21 and to identify and posttraumatic changes subjects. J Neurol Neurosurg Psychiatr 1983;46:681-683. or space-occupying lesions22,52). Recent studies show ultrasound 20. Felsenthal G, Butler DH, Shear MS. Across-tarsal-tunnel motor- to be a promising adjunct to EDX consultation for identifying nerve conduction technique. Arch Phys Med Rehabil 1992;73:64- structural causes of TTS.33,57 69.

14 FOOT AND ANKLE NERVE DISORDERS

21. Finkel JE. Tarsal tunnel syndrome: ankle and foot. Magn Reson 40. Mackinnon SE, Dellon AL. Surgery of the peripheral nerve. New Image Clin North Amer 1994;2:67-78. York: Thieme Medical Publishers; 1988. 22. Frey C, Kerr R. Magnetic resonance imaging and the evaluation of 41. Mann RA. Tarsal tunnel syndrome. Orthop Clin North Am tarsal tunnel syndrome. Foot Ankle 1993;14:159-164. 1974;5:109-115. 23. Galardi G, Amadio S, Maderna L, Meraviglia MV, Brunati L, 42. Murphy PC, Baxter DE. Nerve entrapment of the foot and ankle in Dal Conte G, Comi G. Electrophysiologic studies in tarsal tunnel runners. Clin Sports Med 1985;4:753-763. syndrome: Diagnostic reliability of motor distal latency, mixed 43. Oh SJ, Lee KW. Medial plantar neuropathy. Neurology nerve and sensory nerve conduction studies. Am J Phys Med 1987;37:1408-1410. Rehabil 1994;73:193-198. 44. Park TA, Del Toro DR. Electrodiagnostic evaluation of the foot. 24. Gatens PF, Saeed MA. Electromyographic findings in the intrinsic Phys Med Rehabil Clin North Amer 1998;9:871-896. muscles of normal feet. Arch Phys Med Rehabil 1982;63:317-318. 45. Park TA, Del Toro DR. The medial calcaneal nerve: anatomy and 25. Goodman CR, Kehr LE. Bilateral tarsal tunnel syndrome. J Am nerve conduction technique. Muscle Nerve 1995;18:32-28. Podiatr Assoc 1983;73:256-260. 46. Pollock LJ, Davis L. Peripheral nerve injuries. New York: Paul B. 26. Gumbine NA, Radovic PA, Parsons R, et al. Tarsal tunnel Hoeber, Inc.; 1933. syndrome: comprehensive review of 87 cases. J Am Pod Soc Med 47. Przylucki H, Jones CL. Entrapment neuropathy of muscle branch Assoc 1990;9:457-461. of lateral plantar nerve. J Amer Podiatry Assoc 1981;71:119-124. 27. Hamm JT, Sanders M. Anatomic variations of the nerve to the 48. Rask MR. Medial plantar neurapraxia (“jogger’s foot”): report of abductor digiti quinti muscle. Foot Ankle 1987;8:123. three cases. Clin Orthop Rel Res 1978;134:193-195. 28. Havel PE, Ebraheun NA, Clark SE, et al. Tibial nerve branching in 49. Reade B, Longo D, Keller M. Tarsal tunnel syndrome: chronic the tarsal tunnel. Foot Ankle 1988;9:117-119. ankle pain. Clin Podiatr Med Surg 2001;18:395-408. 29. Heimkes B, Posel P, Stolz S, Wolf K. The proximal and distal tarsal 50. Roegholt MN. Een nervus calcaneus inferior als overbrenger van tunnel syndromes: An anatomical study. Int Orthop 1987;11:193- de pijn bij calcaneodynie of calcanensspoor en de daaruit volgende 196. therapie. Ned Tijdschr v Geneeskd 1940;84:1898. 30. Irani, KD, Grabois M, Harvey SC. Standardized technique for 51. Saeed MA, Gatens PF. Compound nerve action potentials of the diagnosis of tarsal tunnel syndrome. Am J Phys Med 1982;61:27- medial and lateral plantar nerves through the tarsal tunnel. Arch 31. Phys Med Rehabil 1982;63:304-307. 31. Johnson EW, Ortiz PR. Electrodiagnosis of tarsal tunnel syndrome. 52. Saeed MA. Tarsal tunnel syndrome. In: Course C: Painful foot and Arch Phys Med Rehabil 1966;47:776-780. ankle. AAEM 51st Annual Scientific Meeting. Savannah, Georgia; 32. Keck C. The tarsal tunnel syndrome. J Bone Joint Surg November 2004. pp 17-26. 1962;44A:180-184. 53. Sarrafian SK. Anatomy of the foot and ankle. Philadelphia: JB 33. Kim E, Childers MK. Tarsal tunnel syndrome associated with Lippincott; 1983. a pulsatile artery: effectiveness of high-resolution ultrasound 54. Spindler HA, Reischer MA, Felsenthal G. Electrodiagnostic in diagnosing tarsal tunnel syndrome. Am Podiatr Med Assoc assessment in suspected tarsal tunnel syndrome. Phys Med Rehabil 2010;100:209-212. Clin North Amer 1994;5:595-612. 34. Kraft GH. Tarsal tunnel entrapment. In Course E: Entrapment 55. Tanz SS. Heel pain. Clin Orthop 1963;28:169-177. neuropathies. AAEE Ninth Annual Continuing Education Course, 56. Troni W, Parino E, Pisani PC, Pisano G. Segmental analysis of Boston. September 25, 1986, pp 13-18. motor conduction block in distal tracts of the tibial nerve: a coaxial 35. Lam SJS. A tarsal-tunnel syndrome. Lancet 1962;2:1354-1355. needle electrode study. Clinical Neurophys 2010;121:221-227. 36. Lau JC, Daniels TR. Tarsal tunnel syndrome: a review of the 57. Vijayan J, Therimadasamy AK, Teoh HL, Chan YC, Wilder-Smith literature. Foot Ankle Int 1999;20:201-209. EP. Sonography as an aid to neurophysiologic studies in diagnosing 37. Linscheid RL, Burton RC, Fredericks EJ. Tarsal-tunnel syndrome. tarsal tunnel syndrome. Am J Phys Med Rehabil 2009;88:500- South Med J 1970;63:1313-1323. 501. 38. Liveson JA, Ma DM. Laboratory reference for clinical 58. Wiechers D, Guyton JD, Johnson EW. Electromyographic findings neurophysiology. Philadelphia: FA Davis; 1992. in the extensor digitorum brevis in a normal population. Arch Phys 39. Mackinnon SE, Dellon AL, Daneshvar A. Tarsal tunnel syndrome: Med Rehabil 1976;57:84-85. histopathologic examination of a human posterior tibial nerve. 59. Zaza DI, Del Toro DR, White KT. A retrospective review of isolated Contemp Orthop 1984;9:43-48. tibial neuropathies in the foot. Muscle Nerve 2006;34:517.

15 16 First Branch Lateral Plantar Neuropathy: “Baxter’s Neuropathy”

David R. Del Toro, MD Associate Professor Department of Physical Medicine and Rehabilitation Medical College of Wisconsin Milwaukee, Wisconsin

INTRODUCTION quinti pedis (ADQP) muscle in the foot, was first described by Roegholt in 1940.31 This nerve branch has been given other desig- The awareness and appreciation of the details of a first branch lateral nations in the literature which are quite specific and anatomically plantar neuropathy (hereafter referred to as Baxter’s neuropathy) descriptive, including the first branch of the LPN,2,3,32,37,39 “nerve in the foot requires that an electrodiagnostic (EDX) physician to the abductor digiti quinti”3,18,25,30,37 and “muscular branch of the must first have a comprehensive and accurate understanding of LPN to the abductor digiti quinti muscle.”32 The title “Baxter’s the tibial nerve and its branching pattern in the ankle and foot. nerve” is an informal term and is named for a pioneering orthope- Therefore, this discussion emphasizes that thorough knowledge dic surgeon2,3,4 who had conducted a great amount of clinical and of the neuroanatomy of the foot and ankle is fundamentally research activity related to this nerve. There have been numerous crucial in the EDX evaluation and subsequent diagnosis of citations in the orthopedic2,3,4,11,14,21,24,25,32,35,36,37 and podiatric1,30 lit- distinct mononeuropathies in the foot. Initial background material erature reporting Baxter’s neuropathy as a relatively common and will focus on the first branch (also called “Baxter’s nerve”) of treatable cause of heel pain syndrome. One of the primary reasons the lateral plantar nerve (LPN) and the relevant past literature for distinguishing this nerve entrapment disorder as being differ- regarding this nerve, followed by details of the neuroanatomy ent from classic TTS and other tibial branch mononeuropathies in of the foot and ankle, particularly concentrating on the tibial the foot is the anatomic course of Baxter’s nerve, which is quite nerve and its functional terminal branches. Then, details of the dissimilar compared to the medial plantar nerve (MPN) and LPN clinical presentation (including signs and symptoms) and the in the foot and the medial calcaneal nerve (MCN) in the heel. The EDX evaluation will be presented, as it pertains to Baxter’s anatomic comparison between these tibial nerve branches will be neuropathy and, in general, other mononeuropathies in the foot. detailed below. Finally, in the discussion, the author stresses the critical EDX and anatomic factors in distinguishing Baxter’s neuropathy from other NEUROANATOMY tibial branch neuropathies in the foot, particularly tarsal tunnel syndrome (TTS). In addition, a case report of Baxter’s neuropathy From this author’s viewpoint, functionally, the tibial nerve has is presented. four terminal branches: the MCN, the MPN, the LPN, and Baxter’s nerve (Fig. 1). This is based on their discrete anatomic course and BACKGROUND different sites of entrapment within the foot. All of these tibial nerve branches pass through the proximal tarsal tunnel but then Baxter’s neuropathy is considered to be a nerve entrapment dis- their individual courses begin to diverge. The MCN, believed to order in the foot involving compression of the inferior calcaneal be a purely sensory nerve, has an extremely variable origin but nerve (i.e., the first branch of the LPN). The inferior calcaneal relatively consistent terminal course and usually pierces the flexor nerve, the nerve which ultimately innervates the abductor digiti retinaculum of the tarsal tunnel (Fig. 1) to provide cutaneous 17 First Branch Lateral Plantar Neuropathy : “Baxter’s Neuropathy” innervation to the posterior, medial, and plantar surfaces of the heel (Fig. 2).27,34 The different mechanisms of MCN entrapment include a tight fascial layer overlying the MCN,39 chronic external injury (such as a patient’s shoe rubbing against a prominent os calcis), or possibly due to excessive pronation.5 In the distal tarsal tunnel the interfascicular septum (IFS) is formed by the deep fascia of the abductor hallucis (AH) muscle and this septum separates the MPN and LPN into the upper and lower calcaneal chambers, respectively. Both of these nerves, the MPN and LPN, are mixed nerves which supply motor, cutaneous, articular, and vascular branches in the foot. The details of the anatomic course for both the MPN and LPN and their distinct sites of entrapment in the foot are discussed in a separate section of this course.

In discussing the anatomic course of Baxter’s nerve, one must first

Baxter’s nerve realize that while it travels through the tarsal tunnel, it typically comes off distal to the MCN origin, and then within the distal tarsal tunnel it usually branches off the LPN (hence, the term first Figure 1. Medial aspect of right foot. Note that Baxter’s nerve, usually the branch of the LPN) but sometimes may branch from the tibial ner first branch off the LPN, in this case, branches off the tibial nerve but still ve.1,3,4,7,9,17,18,23,30,32,34,36 After this branch point, Baxter’s nerve then eventually lies deep to the AH. Also, the MCN branches pierce the FR as exits the posterior aspect of the lower calcaneal chamber, passing they course towards the medial/plantar aspect of the heel. between the thick investing, taut deep fascia of the AH (medially) AH = abductor hallucis muscle, FR = flexor retinaculum, IFS = interfascicular and the quadratus plantae (laterally) (Fig. 3).34 Next, at the level of septum, LPN = lateral plantar nerve, MCN = medial calcaneal nerve, MPN the inferior border of the AH deep fascia, Baxter’s nerve crosses = medial plantar nerve, QP = quadratus plantae muscle, TN = tibial nerve laterally in nearly a transverse fashion immediately anterior to the Adapted with permission from Park and Del Toro.28a medial calcaneal tuberosity (Fig. 4) to pass between the underlying quadratus plantae and the overlying flexor digitorum brevis (Fig. 3). Along its proximal course, Baxter’s nerve usually will give off periosteal sensory branches to the medial calcaneal tuberosity,1,34 a branch into the long plantar ligament and may send motor 1 branches to the quadratus plantae and flexor digitorum brevis 2 (Fig. 5).7,36 Finally, numerous anatomic dissection studies have demonstrated that Baxter’s nerve always terminates with motor branches to the ADQP1,4,7,8,30,32,36 (also known as the abductor digiti minimi muscle). Furthermore, of the four terminal tibial nerve branches in the foot, Baxter’s nerve is the only one that 3 does not to have any cutaneous innervation. 4 CLINICAL PRESENTATION

Because Baxter’s nerve has a distinct anatomic course as compared to the MPN and LPN in the foot, it has completely different sites of entrapment and consequently a somewhat different 6 5 clinical presentation. There are believed to be two major sites of entrapment of Baxter’s nerve after it exits the tarsal tunnel:

• The relatively unyielding space between the deep fascia of the AH and the medial edge of the ADQP, which is the route which Baxter’s nerve follows (Fig. 3).1,2,30,32 Baxter’s nerve may be particularly vulnerable at this site in a pronated foot, because these two muscles are forced together more firmly, consequently placing greater traction on this nerve.36 Figure 2. Cutaneous innervation of the plantar aspect of the foot. • The anterior calcaneus and in particular the medial calcaneal 1 = medial calcaneal nerve, 2 = lateral calcaneal nerve, 3 = saphenous tuberosity, especially if there is a heel spur present (Fig. nerve, 4 = sural nerve, 5 = medial plantar nerve, 6 = lateral plantar nerve 4).2,25,30,39 Baxter’s nerve is believed to be vulnerable for Adapted with permission from Sarrafian.34 entrapment at this site because it passes immediately in front of the anterior calcaneus, with a mean distance between this nerve and the medial calcaneal tuberosity of approximately 5.5 mm.1,17 Therefore, due to this intimate anatomic relationship, Baxter’s nerve may be injured during surgical 18 FOOT AND ANKLE NERVE DISORDERS removal of an anterior calcaneal heel spur. Additionally, it has been postulated that this site could be clinically significant when there is of surrounding soft tissue structures (e.g., plantar fasciitis) since this would likely impact Baxter’s nerve due to its close proximity.1,39

Clinically, Baxter’s neuropathy usually presents with the predominant symptom of chronic and constant medial/plantar heel pain,2,6,26 while infrequently it can be localized to both the medial and lateral aspects of the heel.26 The pain can be described by various qualities (e.g., dull, aching, throbbing, burning, or sharp) and is often exacerbated by weightbearing activities, such as prolonged walking and standing. The symptoms are precipitated by sports in about 50% of cases and in the author’s Figure 3. Posterior view of the heel showing how Baxter’s nerve passes clinical experience it is often preceded by an established course of between the taut deep fascia of the abductor hallucis (medially) and the plantar fasciitis.2,26 The heel pain in Baxter’s neuropathy however medial edge of the quadratus plantae (laterally). This is a potential site of differs, since it is often worse at night and is essentially constant entrapment for Baxter’s nerve since it is particularly vulnerable to excessive (i.e., present at rest and with weightbearing activities), whereas traction with pronation. in plantar fasciitis there is the hallmark early morning heel pain Adapted with permission from Schon and Baxter.36 that can improve with subsequent stretching, it usually is not constant, and it can improve with rest (i.e., nonweightbearing). Typically, the patient does not report any numbness or tingling in the foot, since Baxter’s nerve has no cutaneous innervation. And, generally speaking, there is no significant complaint of weakness or gait problems, except for antalgic gait due to the characteristic heel pain. Physical examination usually demonstrates marked tenderness over the anteromedial aspect of the heel (or just in front of the medial aspect of the calcaneus).6

According to reports in the literature,16,36 the pathognomonic clinical sign of Baxter’s neuropathy is greater pain with compression over the proximal medial aspect of the heel compared to the plantar aspect. This maneuver should elicit the typical symptoms of burning, shooting, stabbing, tingling, electric, or sharp pain and sometimes there is extension of the pain proximally and distally.36 Furthermore, it is proposed that palpation in this region pinches Baxter’s nerve between the deep fascia of the AH and the medial caudal margin of the quadratus Figure 4. Anatomic course of Baxter’s nerve along the plantar aspect of plantae which results in the pain and possible paresthesia.2 Other the heel. Note that Baxter’s nerve crosses immediately anterior to the examination findings may include inability to abduct the fifth toe, medial calcaneal tuberosity, near the origin of the and also wasting or atrophy of the lateral aspect of the foot in the region the site for a possible heel spur. of the ADQP, and a Tinel’s sign over the anteromedial aspect of Adapted with permission from Baxter and Pfeffer.3 the heel.28,29 Notably, there are no cutaneous sensory deficits, and 26,28,29 muscle stretch reflexes are normal. Plain x-rays demonstrate BranchBranch to to abductor abductor digiti digiti 6 quinti pedis (ADQP) evidence of an anterior calcaneal heel spur in over 50% of cases. quinti pedis (ADQP) Branch to muscle Branch to Also, magnetic resonance images have demonstrated selective medialmedial calcaneal calcaneal tuberosity tuberosity atrophy of the ADQP muscle in Baxter’s neuropathy.10 The tuberosity differential diagnosis should include chronic plantar fasciitis, Baxter’sBaxter’s nerve nerve chronic heel pain syndrome, TTS, Achilles tendinitis/bursitis, medial calcaneal neuropathy, lumbosacral (L-S) radiculopathy or BBranchranch to to flexorflexor digitorum digitorum plexopathy, peripheral polyneuropathy (especially if symptoms brevis muscle Lateral planter brevis muscle nerve nerve Achilles are bilateral), and other conditions not listed here. Medial planter tendon nerve tendon nerve Tibial Medial Some cases of Baxter’s neuropathy will resolve with conservative nerve calcaneal nerve management, which includes nonsteroidal antiinflammatory drugs, nerve shock-absorbing heel cups, a medial longitudinal arch support (for Figure 5. Medial/plantar view of the foot showing the individual branches the excessively pronated foot), and local steroid injection.2,6 After and eventual terminal course of Baxter’s nerve. Note that Baxter’s nerve, approximately 6 months or more of conservative management, if after sending nerve branches to the medial calcaneal tuberosity and the the symptoms fail to resolve, then, surgical decompression may flexor digitorum brevis muscle, then terminates as nerve twigs supplying be indicated. Surgery usually involves release of Baxter’s nerve the abductor digiti quinti pedis muscle. 36 Adapted with permission from Schon and Baxter. 19 First Branch Lateral Plantar Neuropathy : “Baxter’s Neuropathy” between the AH and the quadratus plantae muscles (Fig. 6). This surgical procedure frequently includes incision of the taut deep fascia of the AH, a partial medial plantar fascia release, and a heel Medial calcaneal spur excision, if necessary.2,16,25,30 Following this procedure, 89% nerve of patients report good or excellent results.2 Lateral plantar nerve ELECTRODIAGNOSTIC EVALUATION

Before discussing the specific details in the EDX evaluation of Baxter’s neuropathy, there are several important concepts to consider. In order to do a thorough needle electromyography Baxter’s nerve Abductor hallucis (EMG) examination of the intrinsic foot muscles, the EDX deep fascia physician must learn to sample different muscles from different peripheral nerves within the foot (Table). Plantar fascia These intrinsic foot muscles are chosen frequently by this author Figure 6. The surgical procedure performed for Baxter’s neuropathy due to their specific innervation pattern and because of their includes incision of the deep fascia of the abductor hallucis. superficial location; thus ,they are readily accessible for needle Adapted with permission from Schon and Baxter.36 EMG examination. In the past, a few studies have demonstrated abnormally-prolonged insertional activity in intrinsic foot muscles in a considerable number of normal feet,13,15,40 and, subsequently, many EDX physicians will avoid performing needle EMG examination in the foot because they are unsure on how to interpret these findings. However, these prior studies have either failed to quantitate the observed abnormalities or they demonstrated that these abnormalities, when present, were quite mild.13,15,40 In fact, these studies recorded no actual abnormal spontaneous activity (in the form of sustained positive sharp waves or fibrillation potentials) in any normal subjects. Moreover, in a later study performed in an asymptomatic healthy population, a very low prevalence (i.e., 2% of the study population) was found to have abnormal spontaneous activity, specifically fibrillation potentials, in the intrinsic foot muscles studied.12

These results are consistent with this author’s extensive clinical ADQP FDMB experience in performing EDX studies in the foot. The take home message from the information presented above is that the EDX Figure 7. Lateral view of the foot depicting two different E1 sites in which physician, when interpreting needle EMG findings in the intrinsic both were reportedly recording over the ADQP muscle. (A) E1 site proposed foot muscles, must be careful not to mistake end-plate spikes for by Johnson and Ortiz.20 (B) E1 site proposed by Irani and colleagues.19 abnormal spontaneous activity by paying particular attention to Note that distally, most of the ADQP muscle is tendinous along the lateral the frequency and firing pattern of the observed potentials. Hence, aspect of the fifth metatarsal, while the FDMB muscle belly is immediately this author, as well as others, considers needle EMG examination deep to the ADQP tendon and inferior to the fifth metatarsal. of intrinsic foot muscles an essential component in the EDX ADQP = abductor digiti quinti pedis, FDMB = flexor digiti minimi brevis. evaluation of the foot.23,38 Nonetheless, nerve conduction studies Adapted with permission from Park and Del Toro.28a (NCSs) are still a necessary part of this assessment. However,

Table. Intrinsic foot muscles and the peripheral nerves that innervate them

20 FOOT AND ANKLE NERVE DISORDERS the EDX physician must keep in mind that the tibial motor NCSs indicated clinically) the LPN33 should be performed on the affected (including the MPN, LPN, and Baxter’s nerve) may not show any foot, and, if necessary, on the unaffected foot for comparison. abnormalities with regards to distal onset latency and amplitude Additionally, the MCN conduction technique27 could be employed (either baseline-to-peak or peak-to-peak), even when compared if the clinical presentation suggests MCN involvement. Finally, side-to-side. The reasons for this are likely multifactorial, some NCSs of the sural nerve and the common peroneal (now referred of which are listed here. to as the common fibular) nerve may be included to evaluate for a peripheral polyneuropathy. This is particularly important • The tubular nature of the foot brings all the intrinsic foot if the MPN and/or LPN mixed NCS responses are unobtainable muscles closer together physically and more parallel to or if the motor NCSs of the tibial nerve branches reveal any one another, so it is more likely that a recorded compound abnormalities. muscle action potential (CMAP) represents the summation of potentials from several nearby muscles rather than a Then, the critical needle EMG examination should include, of summated potential dominated by one nearby muscle. course, the ADQP and other intrinsic foot muscles (i.e., the AH, • Since nearly all the intrinsic muscles in the foot (except for fourth dorsal interossei pedis, and EDB) on the affected side, the extensor digitorum brevis [EDB]) are tibial innervated, proximal leg muscles on the same side (e.g., the tibialis anterior, these muscles are activated each time the tibial nerve is medial gastrocnemius, and tensor ), the ipsilateral lower stimulated, thereby magnifying the problem described in the L-S paraspinals to evaluate for L-S radiculopathy or plexopathy, first bullet. and possibly the ADQP (and other intrinsic foot muscles) on the • Because the tibial nerve and its branches (namely the MPN, unaffected side for comparison and to assess for more diffuse LPN, and Baxter’s nerve) follow such a twisting course neurogenic disorders. across the ankle and foot, any measurements that include these nerve branches are likely to be filled with error and In conclusion, typical needle EMG abnormalities in a patient with uncertainty. Baxter’s neuropathy likely would include evidence of ongoing denervation (such as sustained fibrillation potentials and/or Nevertheless, NCSs are an integral part of the EDX evaluation of positive sharp waves) along with possible chronic neurogenic the foot, particularly to assess for peripheral polyneuropathy. changes (such as increased motor unit action potential [MUAP] morphology and duration, increased polyphasic motor units, and/ With these principles in mind, the following would be standard or reduced motor unit recruitment). These needle EMG findings protocol in the EDX evaluation for a patient with suspected would be recorded exclusively from the ADQP muscle of the Baxter’s neuropathy. Motor NCSs should include Baxter’s nerve affected foot.26,28 Needle EMG examination of other ipsilateral (recording over the ADQP)8,20 bilaterally, the MPN (recording intrinsic foot muscles and the contralateral ADQP should be over the AH), and the LPN (recording over the flexor digiti unremarkable. On the other hand, NCSs on the affected side minimi brevis [FDMB])8,19 on the affected side. To clarify, the (including the Baxter’s nerve study) may not demonstrate any recording sites for Baxter’s nerve and the LPN differ: the LPN remarkable abnormalities. motor NCS uses an E1 site over the FDMB at the midpoint of the fifth metatarsal on the lateral aspect of the foot (according DISCUSSION to a previously published technique),19 whereas Baxter’s NCS E1 site is over the ADQP, inferior to the lateral malleolus (Fig. Baxter’s neuropathy as a clinical entity and etiology for heel pain 7). Detailed electrophysiologic mapping of the ADQP CMAP has been well documented in the literature.1,2,3,4,6,11,21,24,25,26,30,32,35,37 revealed that false motor points are very common over the lateral Moreover, in a case series by Ngo and Del Toro, two patients with foot, but they are almost exclusively found anterior to the lateral heel pain were found to have EDX findings consistent with Baxter’s malleolus.8 Based on these electrophysiologic mapping results, for neuropathy and were later confirmed by surgical outcome after a Baxter’s nerve NCS, the author’s recommendation is to place the undergoing release of this nerve.26 Therefore, Baxter’s neuropathy E1 electrode (over the ADQP) inferior and slightly posterior to the along with TTS should always be considered in the differential tip of the lateral malleolus, about halfway between the tip of the diagnosis whenever an EDX physician encounters a patient with lateral malleolus and the sole of the foot (similar to the technique foot pain (and particularly heel pain). Baxter’s neuropathy is previously mentioned).20 Also, Baxter’s nerve conduction study distinct from TTS primarily due to the fact that Baxter’s nerve has parameters were published as follows:8 separate sites of entrapment in the foot as compared to the MPN and LPN. The two principal entrapment sites for Baxter’s nerve Mean onset latency (± 1 SD) = 4.4 (± 0.5) ms in the foot are (1) as it passes between the taut deep fascia of the Mean amplitude (± 1 SD) = 11.0 (± 3.9) mV AH and the ADQP after exiting the tarsal tunnel (Fig. 3) and (2) as it crosses the foot transversely, just immediately anterior to the This author initially becomes suspicious of an electrophysiologic medial calcaneal tuberosity (Fig. 4) while eventually terminating NCS finding if the absolute value is beyond two standard with motor branches destined singularly for the ADQP. deviations of the mean value or if there is greater than 1.5 ms latency difference or greater than 50% drop in amplitude while In the author’s clinical experience with EDX evaluation of using side to side comparison. EDX physicians should realize that tibial branch neuropathies in the foot, the incidence of Baxter’s the most of the time that the Baxter’s nerve CMAP has an initial neuropathy is much higher than that of TTS.41 Also, empirically, downward deflection.8 Continuing with the EDX protocol for the author has found that in cases of “positive” Baxter’s suspected Baxter’s neuropathy, mixed NCSs of the MPN and (if neuropathy that the frequency of abnormal needle EMG findings 21 First Branch Lateral Plantar Neuropathy : “Baxter’s Neuropathy” is much higher compared to abnormal NCS results. One possible 5. Davidson M, Copoloff J. Neuromas of the heel. Clin Pod Med Surg explanation for this is that the Baxter’s nerve CMAP (recording 1990;7:271-288. over the ADQP) is likely a summation of potentials, contributed 6. Davis P, Severud E, et al. Painful heel syndrome: results of from multiple nearby intrinsic foot muscles and not predominantly nonoperative treatment. Foot Ankle Intl 1994;15:531-535. based on the ADQP, due to the unique anatomy of the foot. As 7. del Sol M, Olave E, et al. Innervation of the abductor digiti minimi with any EDX consultation, the EDX physician, utilizing both muscle of the human foot: anatomical basis of the entrapment of clinical and electrophysiologic information for assessment of the abductor digiti minimi nerve. Surg Radiol Anat 2002;24:18- mononeuropathies in the foot, must adhere to logical diagnostic 22. reasoning and internal consistency to deduce that the “best fit” is 8. Del Toro D, Mazur A, et al. Electrophysiologic mapping and the diagnosis of Baxter’s neuropathy. Finally, the key components cadaveric dissection of the lateral foot: Implications for tibial motor in the EDX evaluation of the foot and in diagnosing Baxter’s nerve conduction studies. Arch Phys Med Rehabil 1998;79:823- neuropathy are a sound knowledge of the neuroanatomy of the 826. foot along with an appropriate history and physical examination 9. Didia B, Horsefall A. Medial calcaneal nerve: An anatomical study. in conjunction with the relevant electrophysiologic data which is J Am Podiatr Med Assoc 1990;80:115-119. obtained by a skilled EDX physician. 10. Dirim B, Resnick D, et al. Bilateral Baxter’s neuropathy secondary to plantar fasciitis. Med Sci Monit 2010;16:CS50-53. CASE REPORT 11. Dreeben S, Mann R. Heel pain: sorting through the differential diagnosis. J Musculoskel Med 1992;9:21-37. The following is a case report of a patient with Baxter’s 12. Dumitru D, Diaz C, et al. Prevalence of denervation in paraspinal and neuropathy.26 foot intrinsic musculature. Am J Phys Med Rehabil 2001;80:482- 490. The patient was a 40-year-old white female with a 1-year history 13. Falck B, Alaranta H. Fibrillation potentials, positive sharp waves of left heel pain and plantar fasciitis. She described constant, and fasciculation in the intrinsic muscles of the foot in healthy sharp, throbbing pain over the medial and lateral aspect of the subjects. J Neurol Neurosurg Psychiatry 1983;46:681-683. heel with symptoms exacerbated by weightbearing activities 14. Fuhrmann R, Frober R. Release of the lateral plantar nerve in case and also reported nocturnal pain. She denied any numbness, of entrapment. Oper Orthop Traumatol 2010;22:335-343. tingling, or weakness in the left foot. Physical examination was 15. Gatens P, Saeed M. Electromyographic findings in the intrinsic remarkable for marked tenderness over the medial and medial/ muscles of normal feet. Arch Phys Med Rehabil 1982;63:317-318. plantar aspect (origin of plantar fascia) of the left heel. A Tinel’s 16. Goecker R, Banks A. Analysis of release of the first branch of the sign was present over the medial heel (paresthesia into fourth and lateral plantar nerve. J Am Podiatr Med Assoc 2000;90:281-286. fifth toes). No sensory deficit nor weakness was noted in the left 17. Govsa F, Bilge O, et al. Variations in the origin of the medial and foot and ankle and muscle stretch reflexes were symmetric in both inferior calcaneal nerves. Arch Orthop Trauma Surg 2006;126:6- legs. EDX studies revealed needle EMG findings of 2+ fibrillation 14. potentials and positive sharp waves (along with unremarkable 18. Hamm J, Sanders M. Anatomic variations of the nerve to the MUAP morphology and recruitment) noted exclusively in the abductor digiti quinti muscle. Foot Ankle 1987;8:123. left ADQP but no needle EMG abnormalities in other intrinsic 19. Irani K, Grabois M, et al. Standardized technique for diagnosis of left foot muscles or the right ADQP. Also, NCSs were normal tarsal tunnel syndrome. Am J Phys Med 1982;61:27-31. for Baxter’s nerve bilaterally and both the MPN and LPN (motor 20. Johnson E, Ortiz P. Electrodiagnosis of tarsal tunnel syndrome. and mixed NCSs) in the left foot. Based on the patient’s clinical Arch Phys Med Rehabil 1966;47:776-780. presentation in conjunction with the electrophysiologic findings, 21. Kenzora J. The painful heel syndrome: an entrapment neuropathy. the EDX impression was given as an isolated Baxter’s neuropathy. Bull Hosp Jt Dis Orthop Inst 1987;47:178. After conservative management failed, she underwent surgical 22. Kraft GH. Tarsal tunnel entrapment. In: Miller RG, Shahani BT, decompression of the Baxter’s nerve, which included release of Kraft GH, Wilbourn, AJ. Course E: Entrapment neuropathies. the deep fascia of the AH and a partial release of the plantar fascia. AAEE Ninth Annual Continuing Education Course. Rochester: At followup 10 months postsurgery, excellent outcome was noted Johnson Printing; 1986. as the patient reported “no heel pain” and her prior symptoms 23. Louisia S, Masquelet A. The medial and inferior calcaneal nerves: were essentially resolved. an anatomic study. Surg Radiol Anat 1999;21:169-173. 24. Lutter L. Surgical decisions in athletes’ subcalcaneal pain. Am J REFERENCES Sports Med 1986;14:481-485. 25. Murphy P, Baxter D. Nerve entrapment of the foot and ankle in 1. Arenson D, Cosentino G, et al. The inferior calcaneal nerve: an runners. Clin Sports Med 1985;4:753-763. anatomical study. J Amer Podiatry Assoc 1990;70:552-560. 26. Ngo K, Del Toro D. Electrodiagnostic findings and surgical outcome 2. Baxter D, Pfeffer G. Treatment of chronic heel pain by surgical in isolated 1st branch lateral plantar neuropathy: a case series with release of the first branch of the lateral plantar nerve. Clin Orthop literature review. Arch Phys Med Rehabil 2010;91:1948-1951. Rel Res 1992;279:229-236. 27. Park T, Del Toro D. The medial calcaneal nerve: anatomy and 3. Baxter D, Pfeffer G, et al. Chronic heel pain: treatment rationale. nerve conduction technique. Muscle Nerve 1995;18:32-38. Orthop Clin N Am 1989;20:563-569. 28. Park T, Del Toro D. Case report: isolated inferior calcaneal 4. Baxter D, Thigpen M. Heel pain: operative results. Foot Ankle neuropathy. Muscle Nerve 1996;19:106-108. 1984;5:16-25. 28a. Park T, and Del Toro D. Electrodiagnostic evaluation of the foot. Phys Med Rehabil Clin North Am 1998;9:871-896. 22 FOOT AND ANKLE NERVE DISORDERS

29. Pfeffer G. Plantar heel pain. In: Baxter D. The foot and ankle in 36. Schon L, Baxter D. Heel pain syndrome and entrapment sport. St. Louis: Mosby; 1995. neuropathies about the foot and ankle. In: Gould GS. Operative 30. Przylucki H, Jones C. Entrapment neuropathy of muscle branch of foot surgery. Philadelphia: WB Saunders; 1994. pp 192-208. lateral plantar nerve. J Amer Podiatry Assoc 1981;71:119-124. 37. Schon L, Glennon T, et al. Heel pain syndrome: electrodiagnostic 31. Roegholt M. Een nervus calcaneus inferior als overbrenger van de support for nerve entrapment. Foot Ankle 1993;14:129-135. pijn bij calcaneodynie of calcanensspoor en de daaruit volgende 38. Spindler H, Reischer M, et al. Electrodiagnostic assessment in therapie. Ned Tijdschr v Geneeskd 1940;84:1898. suspected tarsal tunnel syndrome. Phys Med Rehabil Clin North 32. Rondhuis J, Huson A. The first branch of the lateral plantar nerve Amer 1994;5:595-612. and heel pain. Acta Morphol Neerl Scand 1986;24:269. 39. Tanz S. Heel pain. Clin Orthop 1963;28:169-177. 33. Saeed M, Gatens P. Compound nerve action potentials of the medial 40. Wiechers, D, Guyton J, et al. Electromyographic findings in the and lateral plantar nerves through the tarsal tunnel. Arch Phys Med extensor digitorum brevis in a normal population. Arch Phys Med Rehabil 1982;63:304-307. Rehabil 1976;57:84-85. 34. Sarrafian S. Anatomy of the foot and ankle, 2nd ed. Philadelphia: 41. Zaza DI, Del Toro DR, White KT. A retrospective review of isolated JB Lippincott Company; 1993. tibial neuropathies in the foot. Muscle Nerve 2006;34:517. 35. Schon L, Baxter D. Neuropathies of the foot and ankle in athletes. Clin Sports Med 1990;9:489-509.

23 24 Foot Pain Related to Peroneal (Fibular) Nerve Entrapments (Deep and Superficial) and Digital Neuromas Atul T. Patel, MD, MHSA Physiatrist Kansas City Bone & Joint Clinic, PA Overland Park, Kansas

INTRODUCTION ANTERIOR TARSAL TUNNEL SYNDROME

Nerve entrapments in the foot and ankle involve complex anatomic Deep Peroneal Nerve Anatomy structures and often are difficult to diagnose. The clinical symptoms can be vague and electrodiagnostic (EDX) findings may not help After branching from the CPN just distal to the fibular head, in diagnosing the cause of the symptoms. These nerve entrapments the DPN passes through the anterior compartment between the can be due to trauma or repetitive microtrauma. Microtrauma individual muscles of the anterior tibial region. In the leg, the often results from sports-related activity, inappropriate footwear, DPN is a major contributor of the articular branches to the ankle or internal foot derangement. Various lesions that occur in joint.66 Studies by Horowitz,35 and Lawrence and Botte47 revealed the fibro-osseous tunnels can cause nerve compression (e.g., that the DPN divides into medial and lateral branches 1.3 cm ganglion cysts, varicosities, bone and joint abnormalities, tumors, proximal to the mortise (Fig.1). A medial (sensory) branch then tenosynovitis, and hypertrophic muscles). Much of the attention passes directly over the talonavicular joint capsule, while a lateral in electrodiagnosis involving the peroneal nerve has focused on (motor) branch swings laterally to the extensor digitorum brevis compromise of the common peroneal (common fibular) nerve (EDB).47 (CPN) at the fibular head. However, the individual branches of the CPN—the deep peroneal (fibular) nerve (DPN) and superficial Both DPN branches pass deep to the inferior extensor retinaculum peroneal (fibular) nerve (SPN)—can be selectively involved more (IER). The medial branch courses distally in the foot, passing distally in the leg. Because the entrapments of these nerves present an average of 2.9 mm lateral to the first tarsometatarsal joint,47 with a more vague and less dramatic clinical picture than those and crossing beneath the extensor hallucis brevis tendon in the associated with the CPN, they have only infrequently been the forefoot. Before termination as the cutaneous innervation to the subject of studies in the EDX literature. Other causes of foot pain dorsal first webspace, the otherwise sensory medial branch may have been related to interdigital neuromas. The most common of send some motor twigs to the first dorsal interosseus pedis46 in these are Morton’s and Joplin’s neuromas. The purpose of this as many as 92% of feet.3 The lateral branch innervates the EDB discussion is to address compression at the ankle of the DPN and sends articular twigs to multiple joints in the midfoot and (anterior tarsal tunnel syndrome [ATTS]) and the SPN, including forefoot. anatomical considerations, clinical presentation, electrodiagnosis, and treatment. In addition, Morton’s and Joplin’s neuromas will be discussed. 25 Foot Pain Related to Peroneal Nerve Entrapments causes. These include ischemia from decompression illness,65 talar exostoses,23 dorsal foot contusions,51 ganglia on tendons in the tunnel, pes cavus, tight shoe laces, ski boots,42 combat boots, repetitive ankle plantar flexion in ballet dancers, schwannoma,68 the performing of Namaz,4 trauma or posttraumatic changes (such as fractures or inversion-plantar flexion ankle sprains), and traction placed on the DPN under the IER by the “high-heeled shoe” position (toes dorsiflexed and ankle plantar flexed).1,9,15,16,21,46 In addition, isolated entrapment of the medial branch can occur at the first tarsometatarsal joint, either as a result of a bone spur or bony ridge at this site58,62 or through compression by the overlying extensor hallucis brevis tendon.20,39,64

Clinical Presentation Figure 1. Terminal course of the deep peroneal nerve (DPN).Proximal to the inferior extensor retinaculum, the DPN typically divides into a medial ATTS presents with vague, often disabling complaints caused by branch, innervating the first dorsal web space, and a lateral branch, a lesion of the DPN, or one of its branches, at the ankle. Patients’ innervating the extensor digitorum brevis. complaints are mostly sensory in nature, since they rarely notice (From Park TA, Del Toro DR: Electrodiagnostic evaluation of the foot. Phys weakness of the EDB. Aching or tightness over the anterior ankle Med Clin of N Am 9(4):891, 1998. Adapted from Liveson JA: Peripheral and dorsal foot suggests involvement of the lateral branch of the Neurology: Case Studies in Electrodiagnosis, 2nd edition. Philadelphia, FA DPN, whereas numbness and paraesthesias in the first dorsal Davis, 1991, p 53; with permission.) webspace indicate medial branch compromise.5,31,45,46,50 The symptoms may be worse when the patient is at rest9,45 or during weightbearing. Worsening of the pain may cause it to extend proximally into the lower leg.46 The patient may be awakened by the symptoms at night,1,5,9,21,31,45,46,50 relieving them by shaking or moving the affected foot.45

Examination may reveal sensory deficits over the dorsal first webspace if the medial branch is involved.5,9,21,31,45,50 Examination of the lateral branch is more difficult. Even severe isolated weakness of the EDB is nearly impossible to detect clinically, but it is often accompanied by visible atrophy of this muscle when compared to the unaffected foot, thereby giving a clue to lateral branch inv olvement.1,5,9,21,31,45,46,50 The DPN at the IER may display a Tinel’s sign or tenderness to palpation.9,21,45,50 Placing the patient’s foot Figure 2. Optimal E1 site for recording the deep peroneal nerve response in a “high-heeled shoe” position with the toes dorsiflexed and the over the extensor digitorum brevis. The tendons of the extensor digitorum ankle plantar flexed may provoke or reproduce the symptoms.9,50 longus are most easily palpated by having the patient dorsiflex the toes and ankle. The calcaneocuboid ridge is best palpated with the ankle in Electrodiagnostic Studies passive plantarflexion/inversion and the toes relaxed. Electrode placement is approximately 1 cm lateral and 1 cm distal to the junction between Although motor nerve conduction studies (NCSs) of the DPN to the calcaneocuboid ridge and the long extensor tendon to the little toe. the EDB have been described,19,49 anatomic details, particularly (Adapted from Liveson JA, Ma DM: Laboratory Reference for Clinical regarding the placement of E1, are universally vague. Mostly, Neurophysiology. Philadelphia, FA Davis, 1992, p 203; with permission.) these reports call for the positioning of the E1 electrode “over the EDB muscle”19 with no anatomic landmarks given. This technique falls apart in the face of an atrophic muscle, one for which the Mechanism of Compression: Inferior Extensor E1 placement is, unfortunately, the most critical. To remedy this Retinaculum problem, Park and colleagues conducted an electrophysiologic mapping study of the EDB on 10 normal feet, and they matched One or both of the DPN branches can be compromised where they these findings to the anatomy of the foot surrounding this muscle. pass beneath the IER in the anterior ankle. Although this condition They found that there were no false motor points in the EDB of has been named the “anterior tarsal tunnel syndrome,” this is a bit any of these feet, and that the optimal E1 site (based on compound of a misnomer, since there is no actual anatomic “anterior tarsal muscle action potential [CMAP] amplitude) did not coincide with tunnel,” but rather a convex bony surface blanketed by the broad the most prominent point of the EDB belly, determined on each IER.24 foot prior to the mapping study. This optimal E1 site corresponded anatomically to a point 1 cm distal and 1 cm lateral to the Although classic ATTS is due to compression of the DPN as it intersection of the extensor digitorum longus tendon to the little passes deep to the IER, a nearly identical clinical picture can toe and the calcaneocuboid ridge (Figs. 2 and 3). With stimulation result from the compromise of the DPN due to a number of other of the DPN at the ankle, this grid site had a mean distal latency 26 FOOT AND ANKLE NERVE DISORDERS with the smallest standard deviation (4.3 ± 0.7 ms at 8 cm) and also the largest mean CMAP amplitude (7.7 ± 1.6 mV).

The importance of locating the ideal E1 site becomes apparent when considering the high amplitude zone (HAZ) for the EDB. The HAZ is the region over a muscle in which the amplitude of the recorded CMAP is at least 80% of the amplitude of the muscle’s largest CMAP. This ideal recording area for the EDB is much smaller than those of typical intrinsic muscles used for median, ulnar, or tibial nerve motor NCSs.73 Therefore, the examining physician must use particular care when placing the E1 electrode over the EDB, or the amplitude may be erroneously small.

In reports of ATTS, abnormalities for DPN motor NCSs include an abnormally small or delayed CMAP,1,5,9,31,45,46,50 as well as focal Figure 3. Bones of the right foot, showing the relationship between the conduction block with serial “short-segment” stimulation across origin of the extensor digitorum brevis (EDB) and the calcaneocuboid 5 the anterior ankle. ridge. The EDB extends over this ridge on its way to the toes, and the bulk of the muscle is located just distal to the ridge. A sensory NCS technique has been described for the DPN, (Adapted from Chu-Andrews J, Johnson R: Electrodiagnosis: An recording antidromically over the first dorsal webspace while Anatomical and Clinical Approach. Philadelphia, JB Lippincott, 1986; with stimulating above the ankle.19,49 Extensive signal averaging permission.) generally is required and the resulting sensory nerve action potential (SNAP) is extremely small and is, in fact, often too small to record in normal individuals. If this technique is used, it is therefore imperative to perform it on the asymptomatic foot for comparison. A significant side-to-side difference in latency or amplitude suggests compression of the DPN at the ankle.

In an isolated DPN lesion at the ankle, motor and sensory NCSs of the other nerves to the foot, including the SPN, should be normal.

The needle electromyography (EMG) examination technique for Figure 4 Needle approach to the extensor digitorum brevis (EDB). The the EDB often is inadequately described. Some reference books on needle is inserted just medial to the tendon, which is needle EMG leave this muscle out entirely.30 Those that do include prominently displayed when the ankle is actively everted. The angle of the path of the needle is very shallow, taking it across the dorsum of the foot the EDB recommend approaching the muscle perpendicularly, at and beneath the long extensor tendons, thus allowing it to explore the four 12,17 the most prominent point of the muscle belly. This angle fails bellies of the EDB. to consider the flat, fan-shaped geometry of this muscle. A better (Adapted from Liveson JA: Peripheral Neurology: Case Studies in approach is to insert the needle near the lateral edge of the muscle, Electrodiagnosis, 2nd edition. Philadelphia, FA Davis, 1991, p 53; with angling the needle medially over the dorsum of the foot. The permission.) insertion site should be just anterior to the calcaneocuboid ridge, where the main bulk of the muscle is located, and just medial to the peroneus brevis tendon, which is easily palpated near the lateral edge of the foot when the foot is actively everted (Figs. 3 and 4). This technique allows the needle to pass deep to the long extensor tendons and explore all four bellies of the EDB, rather than just the belly to the fourth toe.

Needle EMG findings reported in cases of ATTS have included evidence of denervation in the EDB in the form of prolonged insertional activity, abnormal spontaneous activity,5,19,31,45,50 increased motor unit action potential complexity and duration,5,45 and decreased motor unit recruitment.5,31,45,50 No such abnormalities should be seen in tibial-innervated intrinsic foot muscles, in the EDB of the unaffected foot, or in leg muscles innervated by the Figure 5. Distal course of the superficial peroneal nerve (SPN) and its DPN. terminal branches. Before branching into the medial and intermediate dorsal cutaneous nerves, the SPN exits the deep crural fascia in the lower Although published studies reported prolonged insertional activity leg, a site of entrapment of this nerve. in the EDB in a considerable proportion of normal feet,25,28,75 this (Adapted from Liveson JA, Ma DM: Laboratory Reference for Clinical author has not found this to be the case in his practice. Prolonged Neurophysiology. Philadelphia, FA Davis, 1992, p 203; with permission.) 27 Foot Pain Related to Peroneal Nerve Entrapments insertional activity is seldom seen in normal feet, and frank defect or bulge is often detectable.7,27,40,55 Pain may be provoked spontaneous activity quite rarely, certainly not enough to justify by resisted active ankle dorsiflexion/eversion or by passive ankle deferring needle EMG of the foot on these grounds. plantar flexion/inversion.70,71 There is frequently diminished sensation over the dorsum of the foot.27,40,71 Treatment Electrodiagnostic Studies Conservative management may include changing the patient’s footwear to flat-heeled, more loose-fitting shoes,9,45,46 as well as A number of investigators have described orthodromic and administering a local steroid injection.9,45,46,50 If these measures fail, antidromic NCS techniques for the SPN.49 In addition, Izzo and surgical treatment—consisting of exploration and decompression colleagues36 described an antidromic technique for studying the of the DPN under the IER—can result in improvement of individual medial and intermediate dorsal cutaneous branches symptoms.5,9,45,46,50 separately. More recently, Oh and colleagues60 devised an NCS method that examines the digital twigs of the medial and SUPERFICIAL PERONEAL NERVE ENTRAPMENT intermediate dorsal cutaneous branches with electrodes over the digital twigs to the second and third toes (medial dorsal Superficial Peroneal Nerve Anatomy cutaneous) and the fourth and fifth toes (intermediate dorsal cutaneous branch). This NCS technique can be performed either After leaving the CPN, the SPN courses deep to the peroneal orthodromically or antidromically. muscles in the lateral compartment in the upper third of the leg, although occasionally it can cross instead to the anterior NCS testing should include one or both SPN branches on compartment.2 The SPN then pierces the deep crural fascia the affected side, as well as the unaffected side if needed for approximately 13 cm proximal to the tip of the lateral malleolus comparison. Stimulation electrodes and recording electrodes and divides about 2 cm later into the medial and intermediate should be applied on opposite sides of the SPN exit point from dorsal cutaneous branches2 (Fig. 5). Both of these branches cross the deep fascia. the anterior ankle superficial to the IER on their way to the dorsum of the foot. The medial dorsal cutaneous branch divides into three The needle EMG examination should include at least the SPN- branches that terminate in the dorsum of the first, second, and third innervated muscles (i.e., and peroneus brevis) of toes, while the intermediate dorsal cutaneous branch innervates the affected leg, as well as broader testing to exclude a possible the dorsum of the adjacent sides of the third and fourth toes.66 lumbosacral radiculopathy. Both branches also provide innervation to most of the dorsum of the foot. Diagnostic electrophysiologic findings for superficial peroneal neuropathy may include a prolonged distal latency (or decreased Mechanism of Entrapment: Anterior Fascia of distal nerve conduction velocity)70,71,72 in the affected SPN branch, the Leg although a reduced SNAP amplitude may be more common.21,69 All needle EMG findings typically are normal.21,71 The SPN is vulnerable to entrapment as it exits the deep crural fascia about 13 cm proximal to the lateral malleolus.2 Reported Treatment etiologies include a sharp fascial edge,51 ,71 compression at the exit site due to anterolateral compartment Surgical intervention usually consists of releasing the fascial band syndrome,27,71,72 ankle sprain,40,71 muscle herniation,27,55,71 a at the deep fascial exit,7,40,51,55,63 reducing any muscle herniation, lipoma/fat nodule at the break in the deep fascia,7,71 injury to the or removing any fat nodule.7 A fasciotomy may also be performed SPN during anterior compartment fasciotomy,71,72 and prolonged if there is an associated anterolateral compartment syndrome.27 kneeling and squatting over many years (63). Many of the reported In a report by Styf, 75% of patients remain improved 36 months cases have been in athletes.14,27,55,70 after surgery; the number is lower in athletes.71

Clinical Presentation DIGITAL NEUROMAS ()

SPN entrapment usually presents with smoldering pain over the Morton’s Neuroma lateral ankle and dorsum of the foot. Interestingly, only about one-third of the patients complain of numbness or paresthesias Interdigital neuralgia is a more appropriate term, instead of over the dorsum of the foot.27,51 Often, there is only vague pain neuroma, to describe “Morton’s neuroma.” The pathology involves laterally at about the junction between the middle and distal thirds perineural fibrosis of the common digital nerves of the footas of the leg.7,40 Pain may radiate as far proximally as the .43,51 they pass below the transverse ligament of the metatarsal heads. Symptoms usually worsen with weightbearing7,51,55 and improve There is no interruption of nerve fibers. The condition was first with rest,7,27,55 and they do not tend to worsen at night. Some described by Durlacher in 1845.22 Morton29 in 1876 theorized that patients actually report a localized mass in the distal anterolateral the nerve is compressed between the metatarsal heads. Anatomic leg.27,55 studies have proved that this is not the mechanism responsible for the symptoms, since the interdigital nerve courses plantar Physical examination will show local tenderness27,40,51,71 and a to the transverse intermetatarsal ligament and the metatarsal Tinel’s sign over the fascial exit site.7,27,40,51,70,71 A palpable fascial heads. It was suggested by Nissen59 that the lesion is ischemic 28 FOOT AND ANKLE NERVE DISORDERS in origin, while others have suggested that it is an entrapment neuralgia, but they are helpful in eliminating other causes such as neuropathy.44 Histologic findings of neural changes distal to the more proximal nerve compromise. transverse metatarsal ligament support the theory of transverse intermetatarsal ligament compression of the nerve.32,41 Treatment

The most common location for an interdigital neuroma is between The treatment for these conditions is to unload the forefoot and the third and fourth metatarsal heads (third webspace), but it can allow for healing. This can be achieved by using gel inserts for occur between the other metatarsal heads.26 The second most more optimal force distribution, using wider toe-boxed shoes, common site appears to be the second webspace; however, avoiding high-heeled shoes. Local injections with anesthetic and some have reported that this location is just as frequent as the steroid can be both diagnostic and therapeutic for interdigital third webspace. Interdigital neuromas rarely occur in the first neuromas. They typically do not help with metatarsalgia. For and fourth webspaces.74 Several theories have been proposed to persistent symptoms despite conservative treatment, surgical account for the higher incidence of third webspace neuralgia, excision can be considered. However, the patient needs to realize most on anatomic basis; however, no clear mechanism explains that there is a risk for recurrence. the reason.8,37,48,53 Joplin’s Neuroma The etiologic considerations can be further separated into traumatic and extrinsic factors.52 Trauma from hyperextension “Joplin’s neuroma,” like Morton’s neuroma, is a misnomer and is of the metatarsal phalangeal joints causes greater tethering of more accurately described as digital neuralgia. It is an entrapment the nerve by the transverse metatarsal ligament. This can occur or compression of the plantar proper digital nerve to the hallux in runners and dancers or from wearing high-heeled shoes.52,67 (terminal sensory branch arising from the medial plantar nerve). Extrinsic factors involve any adjacent structures that may Pathological changes in this nerve were first characterized contribute to nerve compromise. Mass effects can occur due to as perineural fibrosis by Joplin in 1971.38 The etiology of the tumors, ganglia, and inflammation, etc.6,10,11,52 condition appears to be trauma, biomechanical imbalances, and direct compression due to accessory bone. The nerve lies Clinical Presentation superficially and is susceptible to injury from direct trauma to the great toe or from chronic compression, as with tight-fitting The symptoms begin insidiously and the patient typically presents shoes. The nerve also could be stretched by bunion deformity or with pain in the region of the metatarsal heads. There may be abnormal pronation of the foot. paresthesias into the affected toes and patients may describe a sensation of a pebble in the shoe. The symptoms worsen with Clinical Presentation loading of the metatarsal heads and compressing the interdigital nerve (e.g., with forefoot weightbearing or squeezing of the toes Patients complain of sharp pain over the medial aspect of the great together in a shoe with a narrow toe box). Occasionally, a click can toe. Also, they may have paresthesias and numbness over the same be appreciated on the examination with palpation of the neuroma area. A thin “cord” can sometimes be felt along the course of the and squeezing of the metatarsal heads together (Mulder’s sign).57 nerve and may even roll when pressure is applied. Other causes Other causes for a similar presentation include metatarsalgia and for a similar presentation include metatarsalgia, stress fractures, injury of the sesamoid bones in the flexor hallucis tendon. The and injury of the sesamoid bones in the flexor hallucis tendon. source of the pain in these conditions is directly from the bones and not in between the metatarsal heads; however, this can be Diagnostic Studies challenging to differentiate clinically. Weightbearing plain radiographs may define malalignment of the Diagnostic Studies toes or degenerative changes. Medial plantar NCSs using surface electrodes with stimulation at the level of the toes and pick up over Weightbearing plain radiographs may define malalignment of the the medial malleolus have been described.33 Oh and colleagues toes or degenerative changes. Ultrasound and magnetic resonance described a technique using a near-nerve needle and signal imaging have been shown to aid in the diagnosis of interdigital averaging to record sensory action potentials orthodromically neuralgia.18,54 Medial plantar NCSs using surface electrodes with from the plantar proper digital nerve to the hallux61 and Cichy and stimulation at the level of the toes and pick up over the medial colleagues13 described the use of Oh’s technique in diagnosing malleolus have been described.33 Oh and colleagues describe a a case with Joplin’s neuroma. Hemmi and colleagues34 have technique using a near-nerve needle and signal averaging to record described a method to assess the distal medial plantar nerve in sensory action potentials orthodromically.61 A selective marked peripheral neuropathy. This technique could be used to assess drop in the amplitude of the compound nerve action potential the medial plantar sensory response orthodromically from the in the involved interdigital nerve was the most characteristic midsole with stimulation of the nerve at the level of the great toe electrophysiological finding. A recent study describes a similar with ring electrodes. technique, but assessing individual digital nerves by using a tape to block recording from the other digital nerve.76 Needle EMG examination findings typically are normal. EDX studies contribute little in the assessment of digital neuralgia, but Needle EMG examination findings typically are normal. EDX they are helpful in eliminating other causes such as more proximal studies contribute little in the assessment of true interdigital nerve compromise. 29 Foot Pain Related to Peroneal Nerve Entrapments

Treatment 14. Daghino W, Pasquali M, Faletti C. Superficial peroneal nerve entrapment in a young athlete: the diagnostic contribution of The treatment for these conditions is similar to that of Morton’s magnetic resonance imaging. J Foot Ankle Surg 1997;36:170-172. neuralgia: using gel inserts to distribute the forces better, wearing 15. Davidson MR. Heel neuroma: identification and removal. J Am wider toe-boxed shoes, and avoiding high-heeled shoes. For Podiatry Assoc 1977;67:431-435. persistent symptoms despite conservative treatment, surgical 16. Day FN 3rd, Naples JJ. Endoscopic tarsal tunnel release: update transposition of the nerve may be considered. 96. J Foot Ankle Surg 1996;35:225-229. 17. Delagi EF, Perotta A, Iazzetti J, Morrison D. Anatomic guide for SUMMARY the electromyographer, 2nd ed. Springfield: Charles C. Thomas; 1980. Foot and ankle neuropathy are frequently underdiagnosed 18. Delfaut EM, Demondion X, Bieganski A, et al. Imaging of foot conditions that involve complex anatomic structures. The primary and ankle nerve entrapment syndromes: from well-demonstrated to difficulty in diagnosing isolated distal entrapment of the DPN, unfamiliar sites. Radiographics 2003;23:613-23. the SPN, or the digital nerves likely is their typically nonspecific 19. DeLisa JA, Lee HJ, Baran EM, Lai KS. Manual of nerve conduction symptoms, and the difficulty in differentiating neuropathy from velocity and clinical neurophysiology, 3rd ed. New York: Raven other clinical entities. These disorders should be kept in mind Press; 1994. whenever a patient complains of vague aching or discomfort in the 20. Dellon AL. Deep peroneal nerve entrapment on the dorsum of the lower leg or ankle. With an accurate knowledge of the anatomy foot. Foot Ankle 1990;11;73-80. of the nerves, one can then bring the diagnosis into clearer focus 21. Dumitru D. Electrodiagnostic medicine. Philadelphia; Hanley & with a clinical assessment that takes the patient’s entrapments into Belfus; 1995. consideration. Appropriate EDX testing, correctly performed, can 22. Durlacher L. A treatise on corns, bunions, the diseases of nails, and then confirm or rule out these diagnostic possibilities. the general management of the feet. London: Simpkin Marshall; 1845. REFERENCES 23. Edlich HS, Fariss BL, Phillips VA, Chang DE, Smith JF, Hartifan C, Edlich RF. Talotibial exostoses with entrapment of the deep 1. Adelman KA, Wilson G, Wolf JA. Anterior tarsal tunnel syndrome. peroneal nerve. J Emerg Med 1987;5:109-113. J Foot Surg 1998;27;299-302. 24. Eibel P. the anterior tarsal tunnel syndrome. J Bone Joint Surg AM 2. Adkison DO, Bosse MJ, Gaccione DR, Gabriel KR. Anatomical 1985;67:170. variations in the course of the superficial peroneal nerve. J Bone 25. Falck B, Alaranta H. Fibrillation potentials, positive sharp waves Joint Surg Am 1991;73:112. and fasciculation in the intrinsic muscles of the foot in healthy 3. Akita K, Sakamoto H, Sato T. Lateromedial and dorsoplantar subjects. J Neurol Neurosurg Psychiatry 1983;46:681-683. borders among supplying areas of the nerves innervating the 26. Fitzgibbons T, Keown B, Sampson C, et al: Foot problems in intrinsic muscles of the foot. Anat Rec 199;225:465-470. athletes. In: Mellion M, ed. Office sports medicine, 2nd ed. 4. Akyuz G, Us, O, Turan B, Kayhan O Canbulat N, Yilmar IT. Phildelphia: Henley and Belfus; 1996. pp 318-336. Anterior tarsal tunnel syndrome. Electromyogr Clin Neurophysiol 27. Garfin S, Mubarak SJ, Owen CA. Exertional anterolateral- 2000;40:123-128. compartment syndrome; case report with fascial defect, muscle 5. Anderson BL, Wetsch JJ, Stewart WA. Anterior tarsal tunnel herniation, and superficial peroneal-nerve entrapment. J Bone Joint syndrome. Arch Phys Med Rehabil 1992;73:1112-1117. 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Borges LF, Hallett M, Selkoe GJ, Welch K. the anterior tarsal tunnel 787. syndrome: A report of two cases. J Neurosurg 1981;54:89-92. 32. Graham CE, Graham DM. Morton’s neuroma: a microscopic 10. Bossley CJ, Cairney PC. The intermetatarsophalangeal bursa— evaluation. Foot Ankle 1984;5:150-153. its significance in Morton’s metatarsalgia. J Bone Joint Surg 33. Guiloff RJ, Scadding JW, Klenerman L. Morton’s metatarsalgia: 1980;62B:184-187. clinical, electrophysiological, and histological observations. J 11. Chandler JT, Davis WH, Anderson RB. Instability of the second Bone Joint Surg Br 1984:586-591. metatarsophalangeal joint presenting as second webspace 34. Hemmi S, Inoue K, et al. Simple and novel method to measure interdigital neuroma. Presented at: 26th Annual Meeting of the distal sensory conduction of the medial plantar nerve. Muscle American Orthopaedic Foot and Ankle Society. Atlanta, Georgia. Nerve 2007;36:307-312. February 25, 1996. 35. Horwitz MT. Normal anatomy and variations of the peripheral 12. Chu-Andrews J, Johnson R. Electrodiagnosis: an anatomical and nerves of the leg and foot. Arch Surg 1938;36:626-636. clinical approach. Philadelphia: JB Lippincott; 1986 36. Izzo KL, Sridhara CR, Rosenholtz H, Lemont H. Sensory conduction 13. Cichy SW, Claussen GC, Oh SJ. Electrophysiological studies in studies of the branches of the superficial peroneal nerve. Arch Phys Joplin’s neuroma. Muscle Nerve 1995;18:671-672. Med Rehabil 1981;62:24-27. 30 FOOT AND ANKLE NERVE DISORDERS

37. Jones JR, Klenerman L. A study of the communicating branch 57. Mulder JD. The causative mechanism in Morton’s metatarsalgia. J between the medial and lateral plantar nerves. Foot Ankle Bone Joint Surg Br 1951;33:94-95. 1984;4:313-315. 58. Murphy PC, Baxter DE. Nerve entrapment of the foot and ankle in 38. Joplin RJ. The proper digital nerve, vitallium stem arthroplasty, runners. Clin Sports Med 1985;4:753-763. and some thoughts about foot surgery in general. Clin Orthop 59. Nissen KI.Plantar digital neuritis: Morton’s metatarsalagia. J Bone 1971;76:199-212. Joint Surg Br 1948;30:84-94. 39. Kanbe K, Kubota H, Shirakura K, Hasegawa A, Udagawa E. 60. Oh SJ, Demirci M, Gajani B, Melo AX, Claussen GC. Distal Entrapment neuropathy of the deep peroneal nerve associated with sensory nerve conduction of the superficial peroneal nerve: new the extensor hallucis brevis. J Foot Ankle Surg 1995;34:560-562. method and its clinical application. Muscle Nerve 2001;24:689- 40. Kernohan J, Levack B, Wilson JN. Entrapment of the superficial 694. peroneal nerve; three case reports. J Bone Joint Surg Br 1985;67:60- 61. Oh SJ, Kim HS, Ahmad BK. Electrophyiological diagnosis of 61. interdigital neuropathy of the foot. Muscle Nerve 1984;7:218-225. 41. Kim JY, Choi JH, Park J, et al. An anatomic study of Morton’s 62. Ort L. Deep peroneal nerve entrapment; a case report. J Foot Surg interdigital neuroma: the relationship between the occurring site 1973;12:20-21. and the deep transverse metatarsal ligament (DTML). Foot Ankle 63. Piza- Katzer H, Pilz E. Compression syndrome of the superficial Int 2007;28(9):1007-1010. fibular nerve. Case report. Handchir Mikrochir Plast Chir 42. Knackfuss IG, Giordano V, Nogueira M, Giordano M. Compression 1997;29:124-126. of the medial branch of the deep peroneal nerve, relieved by 64. Reed SC, Wright CS. Compression of the deep branch of the excision of an os intermetatarseum. A case report. 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31 33 Surgical Management of Entrapment Neuropathies in the Foot, Including Indications and Outcomes

Mark E. Easley, MD Assistant Professor Division of Orthopaedic Surgery Duke University Medical Center Durham, North Carolina

Lew C. Schon, MD Department of Orthopaedic Surgery The Union Memorial Hospital Baltimore, Maryland

INTRODUCTION effect may manifest itself clinically. A typical example is a herni- ated disc creating proximal nerve root impingement and resul- Nerve dysfunction of the foot and ankle is frequently under- tant impairment of axoplasmic flow, exacerbating an otherwise diagnosed because such problems are often poorly localized, asymptomatic mild tibial nerve (TN) compression in the tarsal masked by other injuries, or dynamic in nature. The most im- tunnel. The double-crush syndrome does not necessarily have to portant element in the evaluation of the patient with pain in the involve two distinct areas of nerve compromise; instead, two dif- leg, ankle, or foot is an awareness of these syndromes. The physi- ferent mechanisms of nerve compromise may be responsible for cian should be familiar with the common clinical characteristics the phenomenon. Diabetes mellitus or alcoholism may make a of nerve disorders and possess a sound understanding of the neu- nerve more susceptible to peripheral compression.29,81 roanatomy of the foot and ankle. The aim of this manuscript is to review the major nerve syndromes of the foot and ankle, in- An important factor in the evaluation of nerve disorder of the cluding discussions of etiology, evaluation, and management. lower extremity is that the syndrome may be static or dynamic. A static nerve disorder is present at rest, whereas a dynamic nerve disorder presents only with activity. Frequently, a static examina- OVERVIEW/TERMINOLOGY tion of a dynamic nerve syndrome fails to reveal the patient’s symptoms, whereas an evaluation after exercise or activity which Because of the diffuse nature and often poor localization of nerve produces the symptoms may uncover findings leading to proper pain, evaluation of distal lower extremity nerve symptoms must diagnosis. When assessing a patient with neuralgia or nerve pain, include an assessment of systemic disease, metabolic disorders, it is useful to categorize the neuralgia as nociceptive or ectopic. chemical exposure, medications, alcohol abuse, and other central Nociceptive neuralgia is nerve pain that is induced by mechani- or peripheral neurologic syndromes that may be responsible for cal stimulation, such as touching or twisting. Ectopic neuralgia any pain in the foot and ankle. The double-crush phenomenon is nerve pain that is spontaneous and unprovoked. Although may also be responsible for extremity nerve pain and must be as- ectopic neuralgia may be increased with certain mechanical sessed.18,89,103,104,113 In a double-crush situation, a nerve is affected stresses, clinical manifestation does not depend on these triggers. in two separate locations. Each focus of nerve compromise taken Nerves with ectopic symptoms usually have more internal or in- in isolation may remain subclinical; however, the cumulative trinsic nerve damage than those with nociceptive symptoms.

32 33 SurgicalSurgical Management Management of of Entrapment Entrapment NeuropathiesNeuropathies in in thethe Foot,Foot, Including Including IndicationsIndications andand OutcomesOutcomes (Revised by) Jeffrey A. Mann, MD DepartmentMark E. Easley,of Neurology MD Division of Neuromuscular Diseases Assistant Professor University of Washington Medical Center Division of Orthopaedic Surgery DukeSeattle, University Washington Medical Center Durham, North Carolina Mark E. Easley, MD Assistant Professor Division ofLew Orthopaedic C. Schon, MD Surgery DukeDepartment University of Orthopaedic Medical Surgery Center Durham,The Union NorthMemorial Carolina Hospital Baltimore, Maryland Lew C. Schon, MD Department of Orthopaedic Surgery The Union Memorial Hospital Baltimore, Maryland INTRODUCTION effect may manifest itself clinically. A typical example is a herni- ated disc creating proximal nerve root impingement and resul- Nerve dysfunction of the foot and ankle is frequently under- tant impairment of axoplasmic flow, exacerbating an otherwise diagnosed because such problems are often poorly localized, asymptomatic mild tibial nerve (TN) compression in the tarsal masked by other injuries, or dynamic in nature. The most im- tunnel. The double-crush syndrome does not necessarily have to portant element in the evaluation of the patient with pain in the involve two distinct areas of nerve compromise; instead, two dif- leg, ankle, or foot is an awareness of these syndromes. The physi- ferent mechanisms of nerve compromise may be responsible for cian should be familiar with the common clinical characteristics the phenomenon. Diabetes mellitus or alcoholism may make a of nerve disorders and possess a sound understanding of the neu- nerve more susceptible to peripheral compression.29,81 roanatomy of the foot and ankle. The aim of this manuscript is to review the major nerve syndromes of the foot and ankle, in- An important factor in the evaluation of nerve disorder of the cluding discussions of etiology, evaluation, and management. lower extremity is that the syndrome may be static or dynamic. A static nerve disorder is present at rest, whereas a dynamic nerve disorder presents only with activity. Frequently, a static examina- OVERVIEW/TERMINOLOGY tion of a dynamic nerve syndrome fails to reveal the patient’s symptoms, whereas an evaluation after exercise or activity which Because of the diffuse nature and often poor localization of nerve produces the symptoms may uncover findings leading to proper pain, evaluation of distal lower extremity nerve symptoms must diagnosis. When assessing a patient with neuralgia or nerve pain, include an assessment of systemic disease, metabolic disorders, it is useful to categorize the neuralgia as nociceptive or ectopic. chemical exposure, medications, alcohol abuse, and other central Nociceptive neuralgia is nerve pain that is induced by mechani- or peripheral neurologic syndromes that may be responsible for cal stimulation, such as touching or twisting. Ectopic neuralgia any pain in the foot and ankle. The double-crush phenomenon is nerve pain that is spontaneous and unprovoked. Although may also be responsible for extremity nerve pain and must be as- ectopic neuralgia may be increased with certain mechanical sessed.18,89,103,104,113 In a double-crush situation, a nerve is affected stresses, clinical manifestation does not depend on these triggers. in two separate locations. Each focus of nerve compromise taken Nerves with ectopic symptoms usually have more internal or in- in isolation may remain subclinical; however, the cumulative trinsic nerve damage than those with nociceptive symptoms.

33 34 Surgical ManagementSurgical ofM anagementEntrapment Neuropathies of Entrapment in the Foot, Neuropathies Including Indications in the F andoot Outcomes AAEM Course AAEM Course Painful Foot and Ankle 35

Etiologic considerations apply to all nerves and warrant defini- the branching pattern. Bifurcation of the TN into its two main symptoms has also been related to bony prominences of talocal- authors have had patients jog, exercise, or dance before or during 122 tion. A nerve may be injured by stretch, contusion, or transec- branches, the MPN and the LPN, is typically assessed in refer- caneal coalitions. As noted above, the etiology may be sec- the appointment to expose the symptomatology. Finally, a com- 76 tion. A stretch or contusion may occur as a one-time event or ence to the tarsal tunnel, coursing under the flexor retinaculum ondary to pathology observed only in dynamic situations. prehensive evaluation should include tests to rule out radicu- may happen repetitively. In an overuse nerve syndrome repetitive that spans between the medial malleolus and calcaneus. lopathy (i.e., straight leg raises) or to look for more generalized stretching or contusion may occur numerous times in a subclin- Bifurcation in the tarsal canal occurred in 69-96% and proximal Anatomy findings. ical fashion before manifesting. In more acute traumas, the to the tarsal canal in 4-31% of specimens. The MCN frequently stretch or contusion may present with nerve symptoms immedi- comprises multiple branches, with studies suggesting more than The tarsal canal is a fibroosseous tunnel enclosed by the flexor Diagnostic tests. Radiographs may be helpful in identifying ately or, occasionally, in a delayed fashion. one medial calcaneal branch in up to 60% of specimens. These retinaculum stretching from the posterior aspect of the medial bony deformity, including joint malalignment, coalition, exos- branches may originate both within, proximal to, and distal to malleolus to the posterior process of the talus and calcaneus. The toses, loose bodies/fragments, or even foreign bodies. Further Entrapment syndromes occur either from these overuse mecha- the tarsal canal, and have been shown to stem from the TN, flexor retinaculum is attached to the sheaths of the posterior bony deformity or soft-tissue pathology may be defined with the nisms or it may follow a more acute trauma. In an entrapment MPN, or LPN, although the majority of specimens have tibial, flexor digitorum, and flexor hallucis longus tendons. The use of computed tomography scanning, but magnetic resonance syndrome, a band of tissue external to the nerve (i.e., fascia, demonstrated that the MCN is a branch of the TN. The MPN TN courses within this fibroosseous tunnel with the posterior imaging (MRI) is better in the evaluation of suspected soft-tissue muscle, bone, or scar tissue) impinges on the nerve. When the further divides into plantar branches that innervate intrinsic tibial artery and one of two veins. As noted above, the TN ter- masses or pathology in the tarsal canal. Laboratory studies may scar tissue engulfs the nerve (usually after open trauma, surgery, muscles of the foot and provide plantar sensation. The LPN has minal branches frequently within the tarsal canal, but with a be beneficial in diagnosing systemic causes for TTS and are in- or infection), the condition may be referred to as adhesive neu- similar but more lateral divisions, after giving off its first branch variable pattern. dicated, but may be unreliable. ralgia. Clinical hallmarks of adhesive neuralgia are decreased (FBLPN), which courses anterior to the medial calcaneal range of motion of the adjacent joint and a tender, thickened, or tuberosity and innervates the abductor digiti minimi and occa- Evaluation Electrodiagnostic (EDX) studies, including sensory and motor immobile scar. sionally the flexor brevis. The relative orientation of the various nerve conduction studies (NCSs) and needle electromyography branches varies. In general, the MCN and the FBLPN lie medial History. The patient with TTS may have difficulty localizing (EMG), can be helpful in the assessment of TTS. Evidence of Transection injury may be partial or complete, and it may result to the MPN and LPN. The MPN lies anterior to the LPN. symptoms, but usually describes medial or posteromedial foot entrapment (such as prolonged distal latency and decreased am- in a complete neuroma or in a neuroma in continuity. After any More proximal to the tarsal tunnel, anatomic intercommunica- and ankle pain. The area of pain usually extends along the course plitude) and evidence of axonal damage (such as denervation injury, the territory of the affected nerve can exhibit a variety of tions increase in number and the fascicular bundles become less and distribution of the nerve. Typical symptoms include of radi- findings) on needle EMG can be helpful for prognosis and treat- symptoms: paresthesia (tingling, electric sensations that are not distinct. ation of pain to the plantar aspect of the foot, and occasionally, ment. Although some clinicians suggest that EDX studies are ap- necessarily painful), dyesthesia (painful nerve symptoms), hy- radiation of pain proximally along the medial aspect of the calf. proximately 90% accurate in confirming TTS, other pesthesias (decreased sensitivity), hyperesthesia (increased sensi- Tarsal Tunnel Syndrome The pain, usually characterized as burning, electric, shooting, investigators have noted that these studies fail to correlate with 59,91 tivity), allodynia (nonpainful stimuli resulting in pain stabbing, tingling, or numbing, is generally exacerbated by ac- surgical findings or postsurgical outcome. In a comprehen- 19 perception), or anesthesia (numbness). Loss of afferent nerve Overview tivity and relieved by rest. It is possible that symptoms may be sive review of the literature pertaining to TTS, Cimino con- conduction usually results in a deafferentation phenomenon, present at rest, possibly related to compression created by pos- cluded that, overall, EDX studies are specific, yet insensitive. The which produces more anesthesia in the zone of the damaged af- Although the first description of TN entrapment in the tarsal tural pressure during sleep. The type of activity and specific current authors find that EDX studies should assess not only the ferent nerve and hyperesthesia or dyesthesia in the surrounding canal dates back to 1960, it was not until 2 years later that the movements or positions that exacerbate the pain should be iden- affected nerve, but all of the peripheral nerves in that lower ex- territory. Often, nontraumatized adjacent nerves will be sensitive term tarsal tunnel syndrome (TTS) was introduced. The syn- tified. Finally, any history of systemic disorders that may affect tremity and in the contralateral extremity as well. A complete to palpation because these adjacent nerves carry pain signals drome is defined as compression or compromise of the TN or its nerves must be noted. In addition, trauma, medications, chem- EDX study allows for identification of localized nerve involve- from the damaged territory. The term anesthesia dolorosa refers branches under the posteromedial flexor retinaculum of the ical exposure, alcohol abuse, or low back pain with radiculopa- ment as well as findings suggestive of radiculopathy or peripheral 59 to a zone of numbness that is painful to touch. ankle and foot. Some authors refer to compromise of any of the thy should be documented. neuropathy. TN components as TTS, whereas others distinguish between The five major nerves innervating the foot and ankle are the proximal compression of the TN trunk and more distal com- Physical examination. The patient should be examined in the Management tibial, saphenous, superficial and deep peroneal, and sural pression of terminal nerve branches. To best define clinical enti- weightbearing position to assess overall alignment of the foot nerves. Although compromise may occur at any location along ties and anatomic correlations, syndromes affecting individual and ankle, especially to assess for valgus hindfoot malalignment Nonoperative. Nonoperative measures may prove to be effective the course of a peripheral nerve or its branches (see individual nerve branches will be presented independently in this discus- that may stretch the TN. Claw toe deformities or intrinsic in the treatment of patients with TTS, but are rarely successful nerve sections below), typical foci are recognized and generally sion. wasting may be indicative of advanced TN dysfunction. Any re- if space-occupying lesions are responsible for the symptomatol- 19 related to specific anatomic structures (see individual nerve sec- striction to range of motion of the ankle and hindfoot may be ogy. If inflammation is contributing to nerve compromise, tions below for characteristic syndromes). Etiology indicative of previous injury or degenerative change. Synovitis, nonsteroidal antiinflammatory agents (NSAIDs) may alleviate edema, tendinitis, or venous insufficiency may produce symp- symptoms.19 Occasionally, corticosteroid injections can improve Tarsal tunnel syndrome, or compromise of the TN, may be id- toms from TN irritation. Palpation of the posterior and medial inflammation, especially if the focus of entrapment can be local- TIBIAL NERVE AND BRANCHES iopathic2,31,61,76 but reviews of the literature suggest that a specific aspect of the ankle may identify mass effects of soft-tissues or ized. In most cases, however, relief of symptoms is only tran- 19,76 cause can be identified in up to 82% of patients.19,75,122 even bony prominences or loose bodies. Percussion along the siently. Symptoms in the tarsal tunnel may also result from Anatomy Approximately 33% of the identifiable causes are related to course of the TN may produce paresthesias or dyesthesias in the systemic inflammatory conditions, venous congestion, or pe- trauma or post-traumatic arthritis, including gan- distribution of the TN and its branches. Sensory testing of distal ripheral edema, which often can be managed by addressing the The TN is a component of the , coursing along the glions,64,75,79,121,122 exostoses/fracture fragments, scar tissue/fibro- sensory branches using the Semmes-Weinstein monofilaments systemic illness. Occasionally, vitamin B6 may reduce symptoms. posteromedial aspect of the ankle, where it divides into the sis, compartment syndrome after calcaneus fractures,86 and or two-point discrimination may support TN compromise. If Low-dose tricyclic antidepressants (TCAs), such as amitrypti- medial plantar nerve (MPN), lateral plantar nerve (LPN), and valgus hindfoot malalignment producing stretch of the TN.76 the patient complains primarily of symptoms related to specific line, may be used to decrease nerve irritability, but side effects medial calcaneal nerve (MCN) branches. Although the TN con- Other space-occupying lesions include varicosities,35,43 inflam- activities, i.e., an athlete with pain during running, then it may may preclude their efficacy. Gabapentin or other antiepileptic sistently separates into these three main divisions, cadaveric mation related to rheumatologic conditions, tumors 55,87,121 and be helpful for the patient to perform the activity which exacer- drugs may be effective. When TTS is due to tension on the TN studies have demonstrated a considerable amount of variation in anomalous musculature.31,105 The development of tarsal tunnel bates the symptoms before the examination. On occasion, the from excessive pronation of the foot, then modification of

34 AAEM Course FOOT ANDPainful ANKLE Foot NERVE and Ankle DISORDERS 35 symptoms has also been related to bony prominences of talocal- authors have had patients jog, exercise, or dance before or during caneal coalitions.122 As noted above, the etiology may be sec- the appointment to expose the symptomatology. Finally, a com- ondary to pathology observed only in dynamic situations.76 prehensive evaluation should include tests to rule out radicu- lopathy (i.e., straight leg raises) or to look for more generalized Anatomy findings.

The tarsal canal is a fibroosseous tunnel enclosed by the flexor Diagnostic tests. Radiographs may be helpful in identifying retinaculum stretching from the posterior aspect of the medial bony deformity, including joint malalignment, coalition, exos- malleolus to the posterior process of the talus and calcaneus. The toses, loose bodies/fragments, or even foreign bodies. Further flexor retinaculum is attached to the sheaths of the posterior bony deformity or soft-tissue pathology may be defined with the tibial, flexor digitorum, and flexor hallucis longus tendons. The use of computed tomography scanning, but magnetic resonance TN courses within this fibroosseous tunnel with the posterior imaging (MRI) is better in the evaluation of suspected soft-tissue tibial artery and one of two veins. As noted above, the TN ter- masses or pathology in the tarsal canal. Laboratory studies may minal branches frequently within the tarsal canal, but with a be beneficial in diagnosing systemic causes for TTS and are in- variable pattern. dicated, but may be unreliable.

Evaluation Electrodiagnostic (EDX) studies, including sensory and motor nerve conduction studies (NCSs) and needle electromyography History. The patient with TTS may have difficulty localizing (EMG), can be helpful in the assessment of TTS. Evidence of symptoms, but usually describes medial or posteromedial foot entrapment (such as prolonged distal latency and decreased am- and ankle pain. The area of pain usually extends along the course plitude) and evidence of axonal damage (such as denervation and distribution of the nerve. Typical symptoms include of radi- findings) on needle EMG can be helpful for prognosis and treat- ation of pain to the plantar aspect of the foot, and occasionally, ment. Although some clinicians suggest that EDX studies are ap- radiation of pain proximally along the medial aspect of the calf. proximately 90% accurate in confirming TTS, other The pain, usually characterized as burning, electric, shooting, investigators have noted that these studies fail to correlate with stabbing, tingling, or numbing, is generally exacerbated by ac- surgical findings or postsurgical outcome.59,91 In a comprehen- tivity and relieved by rest. It is possible that symptoms may be sive review of the literature pertaining to TTS, Cimino19 con- present at rest, possibly related to compression created by pos- cluded that, overall, EDX studies are specific, yet insensitive. The tural pressure during sleep. The type of activity and specific current authors find that EDX studies should assess not only the movements or positions that exacerbate the pain should be iden- affected nerve, but all of the peripheral nerves in that lower ex- tified. Finally, any history of systemic disorders that may affect tremity and in the contralateral extremity as well. A complete nerves must be noted. In addition, trauma, medications, chem- EDX study allows for identification of localized nerve involve- ical exposure, alcohol abuse, or low back pain with radiculopa- ment as well as findings suggestive of radiculopathy or peripheral thy should be documented. neuropathy.59

Physical examination. The patient should be examined in the Management weightbearing position to assess overall alignment of the foot and ankle, especially to assess for valgus hindfoot malalignment Nonoperative. Nonoperative measures may prove to be effective that may stretch the TN. Claw toe deformities or intrinsic in the treatment of patients with TTS, but are rarely successful wasting may be indicative of advanced TN dysfunction. Any re- if space-occupying lesions are responsible for the symptomatol- striction to range of motion of the ankle and hindfoot may be ogy.19 If inflammation is contributing to nerve compromise, indicative of previous injury or degenerative change. Synovitis, nonsteroidal antiinflammatory agents (NSAIDs) may alleviate edema, tendinitis, or venous insufficiency may produce symp- symptoms.19 Occasionally, corticosteroid injections can improve toms from TN irritation. Palpation of the posterior and medial inflammation, especially if the focus of entrapment can be local- aspect of the ankle may identify mass effects of soft-tissues or ized. In most cases, however, relief of symptoms is only tran- even bony prominences or loose bodies. Percussion along the siently.19,76 Symptoms in the tarsal tunnel may also result from course of the TN may produce paresthesias or dyesthesias in the systemic inflammatory conditions, venous congestion, or pe- distribution of the TN and its branches. Sensory testing of distal ripheral edema, which often can be managed by addressing the sensory branches using the Semmes-Weinstein monofilaments systemic illness. Occasionally, vitamin B6 may reduce symptoms. or two-point discrimination may support TN compromise. If Low-dose tricyclic antidepressants (TCAs), such as amitrypti- the patient complains primarily of symptoms related to specific line, may be used to decrease nerve irritability, but side effects activities, i.e., an athlete with pain during running, then it may may preclude their efficacy. Gabapentin or other antiepileptic be helpful for the patient to perform the activity which exacer- drugs may be effective. When TTS is due to tension on the TN bates the symptoms before the examination. On occasion, the from excessive pronation of the foot, then modification of

35 36 Surgical ManagementSurgical Mofanagement Entrapment Neuropathies of Entrapment in the Foot,Neuropathies Including Indications in the F ootand Outcomes AAEM Course activity or use of a medial longitudinal arch support or a stirrup and inadequate release of a portion of the nerve and its branches. brace may be sufficient to relieve symptoms.37 Should nonoper- The third group has no TN scarring and an incomplete release. ative management fail, then consideration may be given to sur- The authors subdivide the first group into cases that (1) never gical intervention.76 experienced temporary relief after the first surgery, (2) experi- enced temporary relief but then recurrence, or (3) became worse Operative. Surgical management of TTS involves release of the and developed new symptoms. flexor retinaculum. Typically, release included the TN and its branches. The tarsal canal should routinely be explored to ensure Evaluation that no masses are responsible for nerve compromise. Neurolysis is not typically performed because doing so may make the nerve Diagnosis is typically made based on history and physical exam- more vulnerable to scarring by disrupting its surrounding bed ination.115 The history is usually consistent with recurrent or and damaging its blood supply. new symptoms described for TTS. Knowledge of the mecha- nism of injury may also be helpful. If there was a space-occupy- Results ing lesion or there had been repetitive trauma, entrapment or an external nerve compression may have been the primary diagno- Several authors have stated that nonoperative management of sis. However, if a crush or stretch injury was noted, the primary TTS is only palliative;35,73,75 however, if a dynamic cause of TN problem may not have been an external nerve problem but an stretch can be identified, then correction of malalignment with internal nerve disorder that may never respond to a release. An use of an orthosis is sometimes successful.19,50,76 Rarely, corticos- important component of the history is a review of the character teroid injection of the tarsal canal is successful in maintaining of the symptoms before previous tarsal tunnel release and a improvement of symptoms.19,50 Tarsal tunnel syndrome due to review of the previous operative report. This information may be space-occupying lesions responds poorly to nonoperative man- useful in defining incomplete previous release or incorrect diag- agement.19 nosis. A history of wound compromise or infection after the initial release is suggestive of new entrapment of the nerve or ad- Review of the literature suggests that surgical tarsal tunnel release hesive neuralgia. results in approximately 60-91% satisfactory results.19,23,50 Results appear to be best when a space-occupying lesion is iden- Although pain may be poorly localized, physical examination tified and removed.76 In the current authors’ experience, results should attempt to find foci of maximum involvement, specifi- are unpredictable when there is no underlying systemic neu- cally with regard to proximal or distal areas of symptoms. ropathy or when the symptoms are exacerbated spontaneously Percussion paresthesias over the scar of the TN release often may without provocation (ectopic neuralgia). be indicative of scar formation around the TN, whereas similar findings more distal or proximal to the old incision suggest in- Recurrent Tarsal Tunnel Syndrome complete decompression. A more focal point of paresthesias may indicate a neuroma or neuroma in continuity. A zone of numb- Overview/Etiology ness surrounded by increased nerve sensitivity with proximal trigger points suggests a deafferentation phenomenon, a sign of Previous reports suggest that symptoms may persist in 9-25% of nerve transection. Anesthesia dolorosa or a numb zone that is patients undergoing tarsal tunnel release or recur at variable time painful to touch is also indicative of nerve transection and periods after decompression.19,23,75,76,94,129 Persistent or recurrent neuroma. Decreased and painful range of motion and a thick- pain after previous tarsal tunnel release represents a management ened scar are consistent with adhesive neuralgia. Occasionally, dilemma. Persistence of symptoms may suggest incomplete recurrent or persistent symptoms are associated with vasomotor release, incorrect diagnosis (i.e., nerve not entrapped in tarsal instability; changes in skin temperature, color, or hair; sweating tunnel, more proximal etiology, neuroma in continuity, or true or dryness; sympathetically mediated pain; or chronic region neuroma), systemic neuropathy, or poor technique (i.e., exces- pain syndrome (type II). In these situations, the sympathetic sive nerve trauma during surgery). Recurrence generally is in- system should be addressed initially by sympathetic blockade dicative of scar formation resulting in nerve dysfunction. It has (via medications or injections) to identify the TN compromise been found useful to separate the cases into three categories, fa- by distinguishing between the reactive sympathetic symptoms cilitating management and permitting a more predictable and the primary nerve symptoms. outcome.115 The classification scheme is based on the presence of scar tissue about the TN and the adequacy of decompression of As in primary TTS, EDX studies may be of benefit especially to the trunk and the affected distal branches. The first group com- localize the nerve pathology, to identify transected nerve prises TNs encased in scar tissue and adequate distal release branches, and to distinguish between external nerve entrapment based on operative report or length of scar. The second group and internal nerve damage. For example, when conduction consists of a combination of TN branches encased in scar tissue delays are found, the diagnosis of entrapment is supported.

36 36 Surgical Management of Entrapment Neuropathies in the Foot, Including Indications and Outcomes AAEM Course AAEM Course FOOT ANDPainful ANKLE Foot NERVE and Ankle DISORDERS 37 activity or use of a medial longitudinal arch support or a stirrup and inadequate release of a portion of the nerve and its branches. Evidence of axonal damage and muscle denervation are sup- rarely results in complete satisfactory improvement of symp- 37 brace may be sufficient to relieve symptoms. Should nonoper- The third group has no TN scarring and an incomplete release. portive of intraneural damage (i.e., neuroma or neuroma in con- toms. ative management fail, then consideration may be given to sur- The authors subdivide the first group into cases that (1) never tinuity).111,115 Although only limited data are available, MRI has 76 gical intervention. experienced temporary relief after the first surgery, (2) experi- been shown promise in identifying factors leading to failed tarsal Results of revision TN release without vein wrap, transection, or enced temporary relief but then recurrence, or (3) became worse tunnel release.129 stimulation can be stratified according to three categories.115 Operative. Surgical management of TTS involves release of the and developed new symptoms. Outcome for neurolysis alone is typically poor when the TN is flexor retinaculum. Typically, release included the TN and its Management encased in scar tissue or when the pathology is a neuroma or branches. The tarsal canal should routinely be explored to ensure Evaluation neuroma-in-continuity.76,115 Some relief of symptoms can be an- that no masses are responsible for nerve compromise. Neurolysis Nonoperative. Nonoperative management of persistent or re- ticipated when the distal release is revised secondary to inade- is not typically performed because doing so may make the nerve Diagnosis is typically made based on history and physical exam- current TTS may be extremely challenging. With persistent or quate decompression.115 The best results are found in patients in 115 more vulnerable to scarring by disrupting its surrounding bed ination. The history is usually consistent with recurrent or recurrent symptoms, the patient has typically failed nonopera- whom persistent or recurrent symptoms are due to inadequate and damaging its blood supply. new symptoms described for TTS. Knowledge of the mecha- tive measures before primary release, and thus it is unlikely that previous distal release alone.76,115 The results of transection, nism of injury may also be helpful. If there was a space-occupy- nonoperative measures will alleviate continued symptoms. wrap, or peripheral nerve stimulation are discussed below. The Results ing lesion or there had been repetitive trauma, entrapment or an However, NSAIDs, TCAs, antiepileptic medications, orthotics, authors’ reported experience with more than 147 revision surg- external nerve compression may have been the primary diagno- and /desensitization (transcutaneous electrical eries for such patients is that vein wrap for adhesive neuralgia, re- Several authors have stated that nonoperative management of sis. However, if a crush or stretch injury was noted, the primary nerve stimulation [TENS] unit) should be attempted before per- vision transection for tibial branch neuromas, and peripheral 35,73,75 TTS is only palliative; however, if a dynamic cause of TN problem may not have been an external nerve problem but an forming revision surgery. Input by pain specialists, who can nerve stimulation for anesthesia dolorosa, ectopic neuralgia, stretch can be identified, then correction of malalignment with internal nerve disorder that may never respond to a release. An provide insight into other effective means of pain control, should deafferentation pain, and the nerve subjected to multiple surg- 19,50,76 use of an orthosis is sometimes successful. Rarely, corticos- important component of the history is a review of the character be considered. A multilodality approach is often warranted. eries have resulted in 80% of the patients realizing 40-50% im- teroid injection of the tarsal canal is successful in maintaining of the symptoms before previous tarsal tunnel release and a provement in pain and function.34,111 19,50 improvement of symptoms. Tarsal tunnel syndrome due to review of the previous operative report. This information may be Operative. The goal of revision surgery is to achieve pain relief space-occupying lesions responds poorly to nonoperative man- useful in defining incomplete previous release or incorrect diag- and improve function. Options for revision surgery include re- 19 agement. nosis. A history of wound compromise or infection after the vision release, revision release with barrier procedure, revision MEDIAL PLANTAR NERVE ENTRAPMENT (JOGGER’S FOOT) initial release is suggestive of new entrapment of the nerve or ad- release with transection and burial of a neuroma, and peripheral Review of the literature suggests that surgical tarsal tunnel release hesive neuralgia. or spinal cord stimulator. The best indications for revision release Overview/Etiology/Anatomy 19,23,50 results in approximately 60-91% satisfactory results. are usually limited to inadequate previous release with focal areas Results appear to be best when a space-occupying lesion is iden- Although pain may be poorly localized, physical examination of nerve irritability.59,76,111,129 Proximally, the TN should be dis- Rask95 introduced the term “jogger’s foot,” referring to isolated 76 tified and removed. In the current authors’ experience, results should attempt to find foci of maximum involvement, specifi- sected free from scar tissue, and distally the abductor hallucis MPN entrapment between the deep fascia of the ABH and the are unpredictable when there is no underlying systemic neu- cally with regard to proximal or distal areas of symptoms. (ABH) fascia should be released to allow for decompression of navicular tuberosity as it courses from beneath the flexor reti- ropathy or when the symptoms are exacerbated spontaneously Percussion paresthesias over the scar of the TN release often may the MPN, LPN, and FBLPN.76,115,129 Occasionally, preoperative naculum toward the master knot of Henry. Typically this syn- without provocation (ectopic neuralgia). be indicative of scar formation around the TN, whereas similar assessment suggests involvement of the MCN, which should drome is associated repetitive stress of the nerve in runners or findings more distal or proximal to the old incision suggest in- also be released. Neuromas should be identified and transected military recruits, often with excessive hindfoot valgus and hy- Recurrent Tarsal Tunnel Syndrome complete decompression. A more focal point of paresthesias may more proximally and/or buried into fat, muscle, or bone. If the perpronation of the foot.85,117 Although medial arch supports indicate a neuroma or neuroma in continuity. A zone of numb- TN has been transected, a cable graft or vein tube graft may be may improve foot alignment, they may exacerbate symptoms by Overview/Etiology ness surrounded by increased nerve sensitivity with proximal considered. In the presence of adhesive neuralgia, revision release further compressing the MPN.108 trigger points suggests a deafferentation phenomenon, a sign of with a barrier procedure, such as a vein wrap, is warranted. For Previous reports suggest that symptoms may persist in 9-25% of nerve transection. Anesthesia dolorosa or a numb zone that is a patient with ectopic neuralgia, anesthesia dolorosa, or deaf- Kopell and Thompson66 theorized that MPN entrapment is as- patients undergoing tarsal tunnel release or recur at variable time painful to touch is also indicative of nerve transection and ferentation phenomenon, neurostimulation should be consid- sociated with hallux rigidus, as the patient attempts to lift the 19,23,75,76,94,129 periods after decompression. Persistent or recurrent neuroma. Decreased and painful range of motion and a thick- ered. For a patient with diffuse nerve symptomatology, especially arch with tibialis anterior overactivity. Furthermore, denervation pain after previous tarsal tunnel release represents a management ened scar are consistent with adhesive neuralgia. Occasionally, one who does not respond to a nerve block, spinal cord stimula- of the forefoot in the distribution of the MPN by this mecha- dilemma. Persistence of symptoms may suggest incomplete recurrent or persistent symptoms are associated with vasomotor tion is preferable to peripheral neurostimulation. Patients with nism led to greater hallux metatarsophalangeal (MTP) joint de- release, incorrect diagnosis (i.e., nerve not entrapped in tarsal instability; changes in skin temperature, color, or hair; sweating severe focal TN involvement are candidates for peripheral nerve generation.66 Although possible, this relationship has not been tunnel, more proximal etiology, neuroma in continuity, or true or dryness; sympathetically mediated pain; or chronic region stimulation. Should a major component of sympathetically me- substantiated by any other study. neuroma), systemic neuropathy, or poor technique (i.e., exces- pain syndrome (type II). In these situations, the sympathetic diated pain be apparent, then surgery and postoperative man- sive nerve trauma during surgery). Recurrence generally is in- system should be addressed initially by sympathetic blockade agement should include the use of a continuous sympathetic Evaluation dicative of scar formation resulting in nerve dysfunction. It has (via medications or injections) to identify the TN compromise block via epidural catheter. been found useful to separate the cases into three categories, fa- by distinguishing between the reactive sympathetic symptoms History cilitating management and permitting a more predictable and the primary nerve symptoms. Results 115 outcome. The classification scheme is based on the presence of Patients are typically runners with medial arch pain that radiates scar tissue about the TN and the adequacy of decompression of As in primary TTS, EDX studies may be of benefit especially to Results of the management of persistent or recurrent TTS have to the medial three toes.76,108 Occasionally, pain also radiates the trunk and the affected distal branches. The first group com- localize the nerve pathology, to identify transected nerve received little attention in the literature. Reoperation in patients proximally to the medial ankle. The patient may state that prises TNs encased in scar tissue and adequate distal release branches, and to distinguish between external nerve entrapment with recurrent or persistent symptoms after tarsal tunnel release he/she uses orthotic devices for running and that the onset of based on operative report or length of scar. The second group and internal nerve damage. For example, when conduction consists of a combination of TN branches encased in scar tissue delays are found, the diagnosis of entrapment is supported.

37 38 Surgical ManagementSurgical Mofanagement Entrapment Neuropathies of Entrapment in the Foot,Neuropathies Including Indications in the F ootand Outcomes AAEM Course AAEM Course Painful Foot and Ankle 39 symptoms coincided with the use of a new device.76 Symptoms Results coexist, it is difficult to separate the two entities.76 Patients fre- deep fascial layers of the ABH, but also partial medial plantar fa- are typically related to specific activities, especially running, and quently report a history of ineffective management with heel sciectomy.6,8,76,108 Manipulation of the FBLPN should be are relieved by rest.109 No large series of isolated MPN releases is available. Our experi- pain protocols, including NSAIDs, heel cord stretching, heel avoided because it is sensitive to palpation and there may be in- ence, and that of others, suggests that when history and physical pads, and corticosteroid injections. advertent damage to its accompanying fragile vein. Physical Examination examination are consistent with symptoms localized to the MPN, then isolated MPN decompression is successful in reliev- Physical examination. As with all peripheral nerve dysfunction, Results The patient should be viewed in a weightbearing position to ing medial arch pain.76 more proximal compromise should be ruled out with evaluation identify hindfoot valgus and hyperpronation of the foot. The of low back pain, the sciatic nerve, and the TN. Although Results of surgical decompression of the FBLPN suggest satis- patient should also be examined standing on his/her orthotic chronic heel pain symptoms may be diffuse or vague, an under- factory symptomatic relief of chronic heel pain in approximately device to identify any areas of external compression. Palpation LATERAL PLANTAR NERVE ENTRAPMENT standing of the anatomy of the medial and plantar heel fre- 85% of patients.6,8 In cases where evaluation suggests a contri- along the MPN usually reproduces symptoms, consisting of quently permits the examiner to distinguish between symptoms bution of the symptoms from more proximal TN compression, medial arch tenderness and radiation of dyesthesia or paresthesia Isolated LPN entrapment in the tarsal tunnel is rarely discussed; related primarily to nerve entrapment and those related to me- a more extensive tarsal tunnel release should be performed in ad- to the medial three toes. Symptoms may be increased with tight- in the literature, LPN compromise is typically considered as part chanical symptoms of plantar fasciitis. The most common sites dition to this distal decompression.9 ening of the ABH muscle, which can be accomplished with a of TTS or as an FBLPN entrapment (discussed below). of nerve entrapment between the ABH, QP, and the flexor dig- heel rise or eversion of the heel. Because of the close proximity However, Kaplan and Kernahan59 noted that the LPN may be itorum brevis are located proximal to the typical location of ten- Calcaneal Branches of the MPN and the toe flexors, distinguishing between neural- most vulnerable to entrapment in the tarsal canal because of its derness of the plantar fasciitis.9,76,108 Symptoms may be gia and tendinitis may be difficult. Usually, tenosynovitis is iden- oblique course in a separate tunnel under the ABP hallux. reproduced by everting the foot. Occasionally, weakness of the Overview/Etiology/Anatomy tified by forced toe plantarflexion against resistance or passive Electrodiagnostic studies for tarsal tunnel have supported this adductor digiti quinti may be apparent. In distinction to cal- hyperextension, which should not produce neurologic symp- finding, because conduction compromise in TTS most fre- caneal stress fracture, FBLPN entrapment does not produce ten- The medial calcaneal branches of the TN provide sensation on toms.108 Occasionally, it may be necessary to have a patient run quently involves the LPN fibers.9 derness to palpation over the lateral wall of the calcaneus or over the medial aspect of the heel. Anatomic studies have demon- on a treadmill for several minutes to identify symptomatology.109 the posterior calcaneal tuberosity. strated a proximal origin of the MCN branches from the TN First Branch (“Baxter’s Nerve”) and the existence of multiple MCN branches;25,28,51 one study Diagnostic Studies Diagnostic studies. Anesthetic nerve blocks may be adminis- showed that 70% of MCNs originated proximal to the tarsal Overview/Etiology/Anatomy tered, but they offer little information in distinguishing between tunnel and that 60% of specimens had multiple branches.25 Weightbearing radiographs define the bony architecture and mechanical symptoms of plantar fasciitis and nerve symptoms Compromise of the MCN branches may contribute to chronic possibly may perinavicular arthritis or loss of medial column Although TTS may produce symptoms in the distribution of the related to the FBLPN. Electrodiagnostic studies, however, have heel pain.9,54,100,123 The MCN branches do exhibit a considerable alignment. These latter two findings suggest primary muscu- FBLPN, entrapment of the FBLPN should be viewed as an in- proven useful in the evaluation of chronic heel pain. Schon and amount of variation in terms of location, origin, and course. An loskeletal pathology as the etiology of the symptoms. dependent entity.6,53,107 The close proximity of this nerve to the colleagues112 demonstrated that needle EMG or NCSs are sensi- MCN may occasionally originate from the MPN.25,51,112 Electrodiagnostic studies may be helpful in identifying medial plantar fascia has implicated FBLPN compression as being re- tive in detecting plantar nerve functional abnormalities in pa- plantar neuralgia, but because the syndrome is dynamic, such a sponsible for symptoms in 10-20% of patients with chronic heel tients with chronic heel pain. A technetium bone scan will Some studies have demonstrated that calcaneal “neuromas” may static study typically contributes very little to the assessment. pain.6-8,112 frequently show plantar medial tuberosity uptake with plantar produce a painful heel syndrome;21,24,41 however, most likely Electrodiagnostic evaluation may detect a more proximal com- fasciitis or calcaneal stress fracture. such a painful heel syndrome secondary to MCN compromise pression that has produces MPN symptoms.108 The FBLPN travels obliquely between the deep fascia of the occurs only when a true MCN neuroma resulted from a tran- ABH muscle and the quadratus plantae (QP), after which it Management section injury during previous surgery.112 With an accessory Management courses laterally to separate into three branches, which supply muscle (i.e., soleus or flexor hallucis longus), we have seen symp- the medial calcaneal periosteum, the flexor brevis, and the ab- Nonoperative. Nonoperative management is essentially the tomatic tenting of the MCN over the bulky muscle. Nonoperative ductor digiti quinti. The branch to the medial calcaneal perios- same as that for TTS. However, because of the overlap with me- teum has been shown to also innervate the QP. Entrapment chanical symptoms, patients are typically treated for plantar Evaluation Activity modification and accommodative shoe wear are usually typically occurs between the ABH and the QP, but it has also fasciitis as well. Corticosteroid injections may prove to be bene- recommended in nonoperative management of medial plantar been noted where the nerve traverses the long plantar ligament ficial not only for plantar fasciitis but also in reducing inflam- Confirmation of MCN compression cannot be achieved by neuralgia. Orthotic device modification may provide the neces- or the flexor digitorum brevis. Compression may be exacerbated mation contributing to nerve irritation.108 An ankle/foot standard EDX studies because the MCN is a pure sensory nerve. sary medial support without aggravation of nerve symptoms. by hyperpronation of the foot, ABH hypertrophy, accessory orthosis worn at night may sometimes be beneficial.127 Typically, Testing methods that rely on the patient sensing and expressing Shoe modifications may compensate for hyperpronation so that musculature, or aberrant bursa formations.6,8,22,52,102 nonoperative management is effective in treating chronic heel skin sensitivity to two-point stimulation or irritation may help a lower arched device may be used.108 Occasionally, NSAIDs and pain, although symptoms may persist for more than a year objectify the findings. An accessory muscle or space-occupying cortisone injection may alleviate symptoms.108 Evaluation despite continued nonoperative measures. lesion can be appreciated on computed tomography or MRI scan. Operative History. The patient typically complains of activity-related Operative. For recalcitrant heel pain that has not improved after chronic heel pain that may radiate to the lateral aspect of the foot 6-12 months of nonoperative management, consideration may Management When symptoms are isolated to the MPN, decompression of and/or the medial ankle. The pain is exacerbated by activity, but be given to surgical intervention, especially in the presence of a only the MPN can be performed. Medial plantar nerve release is may be present with the first step in the morning or after rest. positive EDX correlation. The operative procedure involves not As with other syndromes, nonoperative techniques can be used. achieved by release of the ABH fascia and naviculocalcaneal lig- The pain will have a neuritic character that distinguishes it from only decompression of the nerve by release of the superficial and When these fail, surgical management may be considered. ament at the level of the knot of Henry.76,108 the more common plantar fasciitis. When the two conditions

38 38 Surgical Management of Entrapment Neuropathies in the Foot, Including Indications and Outcomes AAEM Course AAEM Course FOOT ANDPainful ANKLE Foot NERVE and Ankle DISORDERS 39 symptoms coincided with the use of a new device.76 Symptoms Results coexist, it is difficult to separate the two entities.76 Patients fre- deep fascial layers of the ABH, but also partial medial plantar fa- are typically related to specific activities, especially running, and quently report a history of ineffective management with heel sciectomy.6,8,76,108 Manipulation of the FBLPN should be are relieved by rest.109 No large series of isolated MPN releases is available. Our experi- pain protocols, including NSAIDs, heel cord stretching, heel avoided because it is sensitive to palpation and there may be in- ence, and that of others, suggests that when history and physical pads, and corticosteroid injections. advertent damage to its accompanying fragile vein. Physical Examination examination are consistent with symptoms localized to the MPN, then isolated MPN decompression is successful in reliev- Physical examination. As with all peripheral nerve dysfunction, Results The patient should be viewed in a weightbearing position to ing medial arch pain.76 more proximal compromise should be ruled out with evaluation identify hindfoot valgus and hyperpronation of the foot. The of low back pain, the sciatic nerve, and the TN. Although Results of surgical decompression of the FBLPN suggest satis- patient should also be examined standing on his/her orthotic chronic heel pain symptoms may be diffuse or vague, an under- factory symptomatic relief of chronic heel pain in approximately device to identify any areas of external compression. Palpation LATERAL PLANTAR NERVE ENTRAPMENT standing of the anatomy of the medial and plantar heel fre- 85% of patients.6,8 In cases where evaluation suggests a contri- along the MPN usually reproduces symptoms, consisting of quently permits the examiner to distinguish between symptoms bution of the symptoms from more proximal TN compression, medial arch tenderness and radiation of dyesthesia or paresthesia Isolated LPN entrapment in the tarsal tunnel is rarely discussed; related primarily to nerve entrapment and those related to me- a more extensive tarsal tunnel release should be performed in ad- to the medial three toes. Symptoms may be increased with tight- in the literature, LPN compromise is typically considered as part chanical symptoms of plantar fasciitis. The most common sites dition to this distal decompression.9 ening of the ABH muscle, which can be accomplished with a of TTS or as an FBLPN entrapment (discussed below). of nerve entrapment between the ABH, QP, and the flexor dig- heel rise or eversion of the heel. Because of the close proximity However, Kaplan and Kernahan59 noted that the LPN may be itorum brevis are located proximal to the typical location of ten- Calcaneal Branches of the MPN and the toe flexors, distinguishing between neural- most vulnerable to entrapment in the tarsal canal because of its derness of the plantar fasciitis.9,76,108 Symptoms may be gia and tendinitis may be difficult. Usually, tenosynovitis is iden- oblique course in a separate tunnel under the ABP hallux. reproduced by everting the foot. Occasionally, weakness of the Overview/Etiology/Anatomy tified by forced toe plantarflexion against resistance or passive Electrodiagnostic studies for tarsal tunnel have supported this adductor digiti quinti may be apparent. In distinction to cal- hyperextension, which should not produce neurologic symp- finding, because conduction compromise in TTS most fre- caneal stress fracture, FBLPN entrapment does not produce ten- The medial calcaneal branches of the TN provide sensation on toms.108 Occasionally, it may be necessary to have a patient run quently involves the LPN fibers.9 derness to palpation over the lateral wall of the calcaneus or over the medial aspect of the heel. Anatomic studies have demon- on a treadmill for several minutes to identify symptomatology.109 the posterior calcaneal tuberosity. strated a proximal origin of the MCN branches from the TN First Branch (“Baxter’s Nerve”) and the existence of multiple MCN branches;25,28,51 one study Diagnostic Studies Diagnostic studies. Anesthetic nerve blocks may be adminis- showed that 70% of MCNs originated proximal to the tarsal Overview/Etiology/Anatomy tered, but they offer little information in distinguishing between tunnel and that 60% of specimens had multiple branches.25 Weightbearing radiographs define the bony architecture and mechanical symptoms of plantar fasciitis and nerve symptoms Compromise of the MCN branches may contribute to chronic possibly may perinavicular arthritis or loss of medial column Although TTS may produce symptoms in the distribution of the related to the FBLPN. Electrodiagnostic studies, however, have heel pain.9,54,100,123 The MCN branches do exhibit a considerable alignment. These latter two findings suggest primary muscu- FBLPN, entrapment of the FBLPN should be viewed as an in- proven useful in the evaluation of chronic heel pain. Schon and amount of variation in terms of location, origin, and course. An loskeletal pathology as the etiology of the symptoms. dependent entity.6,53,107 The close proximity of this nerve to the colleagues112 demonstrated that needle EMG or NCSs are sensi- MCN may occasionally originate from the MPN.25,51,112 Electrodiagnostic studies may be helpful in identifying medial plantar fascia has implicated FBLPN compression as being re- tive in detecting plantar nerve functional abnormalities in pa- plantar neuralgia, but because the syndrome is dynamic, such a sponsible for symptoms in 10-20% of patients with chronic heel tients with chronic heel pain. A technetium bone scan will Some studies have demonstrated that calcaneal “neuromas” may static study typically contributes very little to the assessment. pain.6-8,112 frequently show plantar medial tuberosity uptake with plantar produce a painful heel syndrome;21,24,41 however, most likely Electrodiagnostic evaluation may detect a more proximal com- fasciitis or calcaneal stress fracture. such a painful heel syndrome secondary to MCN compromise pression that has produces MPN symptoms.108 The FBLPN travels obliquely between the deep fascia of the occurs only when a true MCN neuroma resulted from a tran- ABH muscle and the quadratus plantae (QP), after which it Management section injury during previous surgery.112 With an accessory Management courses laterally to separate into three branches, which supply muscle (i.e., soleus or flexor hallucis longus), we have seen symp- the medial calcaneal periosteum, the flexor brevis, and the ab- Nonoperative. Nonoperative management is essentially the tomatic tenting of the MCN over the bulky muscle. Nonoperative ductor digiti quinti. The branch to the medial calcaneal perios- same as that for TTS. However, because of the overlap with me- teum has been shown to also innervate the QP. Entrapment chanical symptoms, patients are typically treated for plantar Evaluation Activity modification and accommodative shoe wear are usually typically occurs between the ABH and the QP, but it has also fasciitis as well. Corticosteroid injections may prove to be bene- recommended in nonoperative management of medial plantar been noted where the nerve traverses the long plantar ligament ficial not only for plantar fasciitis but also in reducing inflam- Confirmation of MCN compression cannot be achieved by neuralgia. Orthotic device modification may provide the neces- or the flexor digitorum brevis. Compression may be exacerbated mation contributing to nerve irritation.108 An ankle/foot standard EDX studies because the MCN is a pure sensory nerve. sary medial support without aggravation of nerve symptoms. by hyperpronation of the foot, ABH hypertrophy, accessory orthosis worn at night may sometimes be beneficial.127 Typically, Testing methods that rely on the patient sensing and expressing Shoe modifications may compensate for hyperpronation so that musculature, or aberrant bursa formations.6,8,22,52,102 nonoperative management is effective in treating chronic heel skin sensitivity to two-point stimulation or irritation may help a lower arched device may be used.108 Occasionally, NSAIDs and pain, although symptoms may persist for more than a year objectify the findings. An accessory muscle or space-occupying cortisone injection may alleviate symptoms.108 Evaluation despite continued nonoperative measures. lesion can be appreciated on computed tomography or MRI scan. Operative History. The patient typically complains of activity-related Operative. For recalcitrant heel pain that has not improved after chronic heel pain that may radiate to the lateral aspect of the foot 6-12 months of nonoperative management, consideration may Management When symptoms are isolated to the MPN, decompression of and/or the medial ankle. The pain is exacerbated by activity, but be given to surgical intervention, especially in the presence of a only the MPN can be performed. Medial plantar nerve release is may be present with the first step in the morning or after rest. positive EDX correlation. The operative procedure involves not As with other syndromes, nonoperative techniques can be used. achieved by release of the ABH fascia and naviculocalcaneal lig- The pain will have a neuritic character that distinguishes it from only decompression of the nerve by release of the superficial and When these fail, surgical management may be considered. ament at the level of the knot of Henry.76,108 the more common plantar fasciitis. When the two conditions

39 40 Surgical ManagementSurgical Mofanagement Entrapment Neuropathies of Entrapment in the Foot,Neuropathies Including Indications in the F ootand Outcomes AAEM Course

Typically, release of the tarsal tunnel with careful release of the space.77 The equal frequency of second and third interdigital MCN is performed. When there is an accessory muscle in- neuromas is supported by a cadaveric study which demonstrated volved, resection of the bulky distal portion is suggested. that the ratios of intermetatarsal head distances to the digital nerve diameters were significantly less in the second and third Results web spaces compared with the first and fourth web spaces.71 In rare instances, both the second and third web spaces may be in- In the authors’ experience with a limited number of cases of volved concurrently.10,30 Interdigital neuralgia very rarely occurs MCN entrapment, good to excellent results can be expected in the first and fourth web spaces.128 Several theories have been 75% of the time. When the nerve has been previously tran- proposed to account for the higher incidence of third web space sected, a more proximal transection and burial is often difficult, neuralgia, most of which have an anatomic basis. Several reports and a centrocentral anastomosis, vein graft, or PNS may be war- suggest that the confluence of medial and lateral nerve fibers ranted.44,111 creates greater thickness of the third interspace common digital nerve, predisposing it to irritation,11,58 a theory that has been refuted by the same cadaveric study noted above.71 Other INTERDIGITAL NEURALGIA (“MORTON’S NEUROMA”) authors have suggested that the relative mobility of the lateral column of the foot compared with the more immobile medial Overview/Etiology/Anatomic Considerations column creates stress on the third common digital nerve.76 However, this theory does not explain the occurrence of a con- The term neuroma is probably a misnomer, because it generally siderable number of second web space .77 refers to interruption of nerve fibers. Interdigital neuralgia, or nerve-related pain, is a more appropriate term for painful afflic- As pointed out by Mann and Baxter,76 etiologic considerations tions of the common digital nerve. This condition was first de- can be separated into anatomic, traumatic, and extrinsic factors. scribed by Durlacher in 1845,33 but it was not until 194011 that Besides the anatomic factors discussed above, the plantar loca- it was considered an entrapment phenomenon caused by the tion of the common digital nerve predisposes it to direct injury. nerve being stretched over the edge of the intermetatarsal liga- Extrinisic factors involve any adjacent structures that may con- ment and anterior edge of the coalesced portion of the plantar tribute to nerve entrapment or compromise. Mann and Baxter76 fascia. Morton82 theorized that the nerve is compressed between have described thickening of the transverse metatarsal ligament, the metatarsal heads. Anatomic studies have proved that this is which may cause nerve compression even without hyperdorsi- not the mechanism responsible for symptoms because the inter- flexion of the MTP joints. Mass effects may occur with ganglia digital nerve courses plantar to the transverse intermetatarsal lig- or tumors, such as lipomas, in the web space. Deviation of the ament and the metatarsal heads. MTP joint due to attenuation of the capsule may diminish the web space or even create traction on the digital nerve. A hyper- The theory of transverse intermetatarsal ligament compression mobile first ray in runners may result in transfer metatarsalgia of the nerve is supported by studies demonstrating that histo- and transfer calluses under the lesser metatarsal heads, creating logic neural changes occur distal to the transverse metatarsal lig- pressure on the common digital nerves. Inflammation in the ament, while neural anatomy proximal to the ligament appears web space may also create nerve compromise. An intermetatarsal normal.46 Specific histologic findings include amorphous bursa has been described by several authors;4,13 it may become eosinophilic material deposition and gradual nerve fiber degen- inflamed, whether or not it is associated with rheumatologic eration. The entrapment phenomenon may be exacerbated by conditions. Typically it is not the mass effect of the bursa, but high-heeled shoes because hyperextension of the MTP joints instead the associated inflammation that is responsible for nerve causes greater tethering of the nerve by the transverse metatarsal dysfunction. Finally, synovitis of the adjacent MTP joint may ligament.76 Such stress on the nerve may account for an in- create inflammation that clinically manifests as interdigital neu- creased incidence of interdigital neuralgia in women. A similar ralgia.17 tethering of the nerve around the transverse metatarsal ligament may occur in athletes involved in activities requiring MTP joint Interdigital neuralgia must be distinguished from other causes of hyperextension (i.e., dancers en pointe or runners rolling plantar forefoot pain, although, as noted above, some forms of through the forefoot).76,109 interdigital neuralgia are a result of adjacent forefoot pathology. The differential diagnosis includes metatarsalgia, MTP joint dis- Most authors have found that interdigital neuralgia is most orders (including degenerative changes, instability, synovitis, in- common in the third web space,11,49 but others state that the flammatory conditions), metatarsal stress fracture, and more condition occurs with equal frequency in the second web proximal nerve compromise.

40 AAEM Course Painful Foot and Ankle 41 40 Surgical Management of Entrapment Neuropathies in the Foot, Including Indications and Outcomes AAEM Course FOOT AND ANKLE NERVE DISORDERS

97,114 36,124 Typically, release of the tarsal tunnel with careful release of the space.77 The equal frequency of second and third interdigital Evaluation sound and MRI have been shown to aid in the diagno- MCN is performed. When there is an accessory muscle in- neuromas is supported by a cadaveric study which demonstrated sis of interdigital neuralgia, another recent study suggested a high volved, resection of the bulky distal portion is suggested. that the ratios of intermetatarsal head distances to the digital History false negative rate when these imaging techniques are correlated 98 nerve diameters were significantly less in the second and third with surgical findings. As these imaging techniques evolve, Results web spaces compared with the first and fourth web spaces.71 In Patients with interdigital neuralgia typically complain of activity- they will most likely contribute substantially to confirming clin- rare instances, both the second and third web spaces may be in- related plantar foot pain between the metatarsal heads. Although ical suspicion when necessary. Electrodiagnostic studies con- In the authors’ experience with a limited number of cases of volved concurrently.10,30 Interdigital neuralgia very rarely occurs a sharp pain or an ache may be present, the pain is generally tribute little in the assessment of true interdigital neuralgia, but MCN entrapment, good to excellent results can be expected in the first and fourth web spaces.128 Several theories have been burning in nature, radiating into the toes. Occasionally, the pain needle EMG and NCSs may elucidate a contribution to the pain 75% of the time. When the nerve has been previously tran- proposed to account for the higher incidence of third web space may radiate proximally to the ankle or produce numbness in the pattern from a proximal nerve compromise. sected, a more proximal transection and burial is often difficult, neuralgia, most of which have an anatomic basis. Several reports toes. A characteristic finding is that the pain is aggravated by and a centrocentral anastomosis, vein graft, or PNS may be war- suggest that the confluence of medial and lateral nerve fibers weightbearing, especially in tight toebox or high-heeled shoes, A helpful diagnostic test is a web-space injection of an anesthetic, ranted.44,111 creates greater thickness of the third interspace common digital and relieved by rest and removal of shoes. As with all the en- inferior to the transverse metatarsal ligament. Relief of symp- nerve, predisposing it to irritation,11,58 a theory that has been trapment syndromes, a history of low back pain or pathology toms from an accurate injection frequently confirms the diagno- refuted by the same cadaveric study noted above.71 Other should also be documented to ensure that symptoms are not sec- sis of interdigital neuralgia. INTERDIGITAL NEURALGIA (“MORTON’S NEUROMA”) authors have suggested that the relative mobility of the lateral ondary to radiculopathy or created by a double-crush phenom- column of the foot compared with the more immobile medial enon. Management Overview/Etiology/Anatomic Considerations column creates stress on the third common digital nerve.76 However, this theory does not explain the occurrence of a con- Physical Examination Nonoperative The term neuroma is probably a misnomer, because it generally siderable number of second web space neuralgias.77 refers to interruption of nerve fibers. Interdigital neuralgia, or The objective of a physical examination is to identify findings Nonoperative management consists of elimination of any factors nerve-related pain, is a more appropriate term for painful afflic- As pointed out by Mann and Baxter,76 etiologic considerations consistent with and responsible for interdigital neuralgia and to that may be contributing to nerve compromise. Wider toebox tions of the common digital nerve. This condition was first de- can be separated into anatomic, traumatic, and extrinsic factors. rule out other diagnoses that may be producing plantar foot shoes, reduction of shoe heel height, softer soled shoes or inserts, scribed by Durlacher in 1845,33 but it was not until 194011 that Besides the anatomic factors discussed above, the plantar loca- symptoms. The patient’s foot should be observed in the weight- and activity modification often prove to be beneficial. Metatarsal it was considered an entrapment phenomenon caused by the tion of the common digital nerve predisposes it to direct injury. bearing position to appreciate any deformity such as toe pads may reduce distal pressure between the metatarsal heads, nerve being stretched over the edge of the intermetatarsal liga- Extrinisic factors involve any adjacent structures that may con- malalignment or web space fullness. Range of motion and stress but occasionally they exacerbate symptoms by creating more ment and anterior edge of the coalesced portion of the plantar tribute to nerve entrapment or compromise. Mann and Baxter76 testing of the MTP joints may suggest degenerative change, syn- proximal pressure on the common digital nerve. Diagnostic fascia. Morton82 theorized that the nerve is compressed between have described thickening of the transverse metatarsal ligament, ovitis, or instability contributing to or mistaken for neural- anesthetic blocks may be combined with corticosteroid injec- 4,88,128 the metatarsal heads. Anatomic studies have proved that this is which may cause nerve compression even without hyperdorsi- gia. Palpation of the web space may occasionally suggest a tions, which have been shown to provide long-term relief of not the mechanism responsible for symptoms because the inter- flexion of the MTP joints. Mass effects may occur with ganglia mass effect such as a ganglion or lipoma; however, such findings symptoms in some patients. However, in patients with symp- digital nerve courses plantar to the transverse intermetatarsal lig- or tumors, such as lipomas, in the web space. Deviation of the are rare. Palpation of the affected plantar interspace(s) typically toms caused by malalignment of the MTP joints, multiple cor- ament and the metatarsal heads. MTP joint due to attenuation of the capsule may diminish the reproduces symptoms consistent with neuralgia; tenderness of ticosteroid injections may lead to additional attenuation of the web space or even create traction on the digital nerve. A hyper- the metatarsal heads suggests metatarsalgia and is not indicative joint capsule and increased nerve compromise. Also, corticos- 84 The theory of transverse intermetatarsal ligament compression mobile first ray in runners may result in transfer metatarsalgia of neuralgia. A Mulder’s sign is an excellent test in the evalua- teroids may create fat pad atrophy, leading to more pressure on of the nerve is supported by studies demonstrating that histo- and transfer calluses under the lesser metatarsal heads, creating tion of interdigital neuralgia. The test is performed by concur- the common digital nerve. logic neural changes occur distal to the transverse metatarsal lig- pressure on the common digital nerves. Inflammation in the rently applying web space pressure distal to the metatarsal heads ament, while neural anatomy proximal to the ligament appears web space may also create nerve compromise. An intermetatarsal and compressing the metatarsal heads transversely. A positive test Operative normal.46 Specific histologic findings include amorphous bursa has been described by several authors;4,13 it may become is documented when a “click” is appreciated and the patient’s eosinophilic material deposition and gradual nerve fiber degen- inflamed, whether or not it is associated with rheumatologic symptoms are reproduced. The click probably represents plantar Surgical intervention is considered for patients who have failed eration. The entrapment phenomenon may be exacerbated by conditions. Typically it is not the mass effect of the bursa, but displacement of tissues between the metatarsals with subsequent nonoperative management. An important diagnostic and prog- high-heeled shoes because hyperextension of the MTP joints instead the associated inflammation that is responsible for nerve impact on impingement on the nerve. However, a click without nostic tool is web space injection of an anesthetic; if complete causes greater tethering of the nerve by the transverse metatarsal dysfunction. Finally, synovitis of the adjacent MTP joint may reproduction of symptoms is not diagnostic of interdigital neu- relief of symptoms is achieved, then nerve resection most likely ligament.76 Such stress on the nerve may account for an in- create inflammation that clinically manifests as interdigital neu- ralgia. The course of the TN from proximal to distal should be will be successful in diminishing the patient’s pain. Surgical creased incidence of interdigital neuralgia in women. A similar ralgia.17 palpated. Although tenderness is usually at or distal to the treatment in patients with more proximal common digital nerve tethering of the nerve around the transverse metatarsal ligament metatarsal heads, more proximal tenderness may be indicative of tenderness or with tarsal tunnel tenderness may require addi- may occur in athletes involved in activities requiring MTP joint Interdigital neuralgia must be distinguished from other causes of a less focal process. Rarely is decreased sensation noted in the tional surgical decisions. When the nerve is tender at or proxi- hyperextension (i.e., dancers en pointe or runners rolling plantar forefoot pain, although, as noted above, some forms of toes affected by the nerve compromise. Finally, as mentioned mal to the metatarsal heads and web site injection at this site through the forefoot).76,109 interdigital neuralgia are a result of adjacent forefoot pathology. previously, evaluation should also include examination to rule alleviates the pain, then resection at that level would be consid- The differential diagnosis includes metatarsalgia, MTP joint dis- out radiculopathy. ered. Most authors have found that interdigital neuralgia is most orders (including degenerative changes, instability, synovitis, in- 77 common in the third web space,11,49 but others state that the flammatory conditions), metatarsal stress fracture, and more Diagnostic Studies Interdigital nerves can be approached from dorsal or plantar in- 11,60,90,99 condition occurs with equal frequency in the second web proximal nerve compromise. cisions. The most commonly described technique in- Weightbearing plain radiographs may define malalignment such volves a dorsal approach through a longitudinal incision with as splay or claw toes or degenerative changes of the forefoot. transection of the intermetatarsal ligament and proximal neurec- Rarely, radiographs may reveal a foreign body. Although ultra- tomy. Current recommendations favor neurectomy 3 cm proxi-

41 42 Surgical Management of Entrapment Neuropathies in the Foot, Including Indications and Outcomes AAEM Course Surgical Management of Entrapment Neuropathies in the Foot mal to the intermetatarsal ligament to ensure that all plantar nerves, or bilateral nerves yields less favorable results. Transection nerve branches are included in the resection.3,128 Other authors of the intermetatarsal ligament without neurectomy has been re- have described a plantar approach through either longitudinal ported to yield approximately 80-85% satisfactory results.27,30,40 incisions between the metatarsal heads or transverse incisions Additional study of patient selection factors and results with this proximal to the metatarsal heads.11,60,90,99 Plantar approaches technique are warranted. may result in a painful scar if performed under or distal to the metatarsal heads and longitudinal plantar incisions frequently create fat pad atrophy and chronic metatarsalgia due to scar hy- RECURRENT INTERDIGITAL NEURALGIA perkeratosis. Richardson and colleagues99 reported favorable on the plantar approach, but observed that wound drainage, plantar Overview/Etiology keratosis, and scar tenderness were the most common complica- tions. A transverse incision proximal to the metatarsal heads Recurrent or persistent interdigital neuralgia is often the results allows for adequate exposure for nerve resection and avoids in- of an incorrect diagnosis rather than a true recurrence.57,76 A terference with the metatarsal heads during weightbearing. more proximal nerve compromise may contribute to the inter- digital symptoms, either completely or as part of a double-crush Several authors have recommended dorsal approach for trans- phenomenon; therefore more proximal areas of compression verse metatarsal ligament transection without neurectomy,27,30,40 should be identified. Occasionally, the incorrect web space may treating the condition as an entrapment syndrome. Although be identified on initial examination, and the surgical procedure this procedure avoids potential recurrent or refractory plantar performed on the incorrect interdigital nerve.56,57 If the pathol- neuroma formation because neurectomy is not performed, there ogy truly was at the web space, then persistent or recurrent is concern that several clinicians have observed reconstitution of symptoms may be secondary to inadequate proximal nerve re- the transverse intermetatarsal ligament.77,128 However, long-term section with neuroma formation in a weightbearing portion of follow-up with this technique suggests that this ligament recon- the forefoot3,10,56,57,76 or inadequate intermetatarsal ligament stitution is probably not clinically significant.40 release. Mann and Reynolds77 and Mann and Baxter76 have also observed an accessory branch or traumatic neuroma that is fre- Postoperatively, a patient is placed in a postoperative shoe and quently missed at the time of primary nerve resection and which may bear weight on the heel. At 2 weeks, sutures are removed. remains under the metatarsal head after resection of the remain- Patients may progress with activity as tolerated but are instructed der of the nerve. that there may be flares of nerve symptoms for several months. Surgical excision of an interdigital nerve obviously results in Evaluation numbness between the affected toes; it is advisable to inform pa- tients of this preoperatively. History

Results Because recurrence or persistence of interdigital neuralgia after surgical resection is frequently due to misdiagnosis, evaluation as It has been estimated that only 20% of patients experience com- described for virgin interdigital neuralgia should be repeated.10,76 plete resolution of symptoms of interdigital neuralgia with non- To administer appropriate management, it is essential to localize operative measures alone.46 Results of corticosteroid injection symptoms, and a review of preoperative symptoms is often suggest that although most patients gain temporary relief of helpful.76 History should include whether or not the patient had symptoms, symptoms are rarely eliminated completely. a symptom-free interval with weightbearing after primary nerve Greenfield and colleagues47 suggested that, in a series of steroid resection. Any associated symptoms, such as radiation of pain injections for suspected interdigital neuralgia, only 30% of pa- from the ankle, leg, or back, should be noted.10 tients had substantial relief over a 2-year period. More recently, Rasmussen and colleagues96 noted that although most patients Physical Examination with third web space neuralgia had relief of symptoms with a single steroid injection, most were still symptomatic. Of the 51 Physical examination of the forefoot may reveal a localized area feet in the study, 50% underwent subsequent surgical resection of tenderness and a positive Tinel’s sign, suggestive of a stump with 96% success; the other 50% remained symptomatic. neuroma.3,57,128 Palpation of the metatarsal heads may be sugges- tive of an accessory nerve branch (as described by Mann and Reports of common digital nerve resection for failed nonopera- Reynolds77 and Mann and Baxter76) or other bony pathology tive management of interdigital neuralgia suggests satisfactory that may be creating nerve impingement. Other forefoot pathol- relief of symptoms in 80-96% of patients.38,77,96 Results appear ogy may be responsible for the pain, and thus other sources of to be best for isolated third web space neuralgia. Resection of iso- AAEMsymptoms Course should be identified, such as MTP joint synovitisPainful or Foot and Ankle 43 lated common digital nerves other than the third, multiple metatarsalgia. Occasionally, interdigital neuralgia is found in ad- jacent web spaces.57 Examination of the tarsal tunnel, lower ex- In a small series of patients, Mann and Reynolds77 and Mann tremity, or the back may unmask areas of more proximal com- and Baxter76 observed that 81% of patients were asymptomatic 42 pression contributing to interdigital symptoms. and 18% were either marginally or not improved after revision surgery through a dorsal approach. Diagnostic Studies

Plain radiographs should be obtained to ensure that no bony ab- SUPERFICIAL PERONEAL NERVE ENTRAPMENT normalities are present that may be responsible for continued nerve compression. Other imaging studies such as MRI or ul- Overview/Anatomy trasound may be suggestive of nerve pathology, but scar tissue from the previous surgical procedure may obscure interpreta- Entrapment of the superficial peroneal nerve (SPN) is not tion. A repeat diagnostic anesthetic block in the affected web common.22,74,80,119 Although it may occur idiopathically, this space may be useful in identifying residual or recurrent distal clinical entity is typically associated with ankle instability,65,74 nerve pathology. Occasionally, evaluation of a neuropathy is in- direct trauma (with associated ganglion),67,116 fibular fracture,9 dicated, including blood tests, nerve studies, or MRIs of the exertional compartment syndrome (and previous fas- spine. ciotomy),119,120 muscle herniation,39,80 lower extremity edema, and (rarely) mass effects such as tumors.5 Probably the most Management meaningful association is that of chronic ankle sprains and per- sistent postinjury anterolateral ankle pain.108 Results of management of recurrent or persistent interdigital neuralgia are typically less successful than those for primary in- Anatomic considerations are important. After branching from terdigital neuralgia.10,57 Nonoperative management should be re- the , the SPN usually courses in the peated, as for a primary interdigital neuralgia with lateral compartment of the leg. It passes through a deep fascial accommodative shoe wear, metatarsal supports, NSAIDS, and tunnel approximately 8-12 cm above the lateral malleolus, after possibly a cortisone injection.10,77 Physical therapy desensitiza- which the nerve divides further into medial and intermediate cu- tion modalities may prove beneficial. taneous branches.1,119 The medial branch supplies sensation to the dorsomedial aspect of the ankle and foot, whereas the inter- As with primary interdigital neuralgia that has failed nonopera- mediate branch is responsible for sensation over the dorsocentral tive management, the approach may be dorsal14,77 or plantar10,57 aspect of the ankle and foot.106 The fibrous tunnel is a site of po- in revision surgery. Proponents of the dorsal approach cite a tential nerve entrapment, as is muscle herniation through the concern for plantar wound complications;77 those preferring a fascial aperture where the nerve leaves the compartment.119 Such plantar incision state that the plantar approach allows for greater herniation may only occur in the dynamic state and be part of a proximal resection of the nerve and avoids dorsal scar tissue from localized “anterior exertional compartment syndrome.” Ankle the previous surgery.10,57 A transverse plantar incision can also be inversion instability may produce a traction injury to the inter- used, as in primary interdigital neuroma resection. mediate cutaneous branch, especially if the nerve is trapped at the site of exit from the deep fascia. Therefore, SPN entrapment Results should be considered in patients with chronic pain after ankle sprain. Occasionally, SPN neuralgia occurs after anterior com- Typically, nonoperative management of recurrent or persistent partment fasciotomy due to reorientation of the fascia, the nerve, interdigital neuralgia/neuroma is palliative.10,57 Mann and and the fibrous tunnel.119 Reynolds77 estimated successful nonoperative management to be between 10 and 20%. Results of revision interdigital nerve re- Evaluation section are less predictable than for primary procedure, with patient dissatisfaction with results after reoperation approaching History 40%.76,77 Beskin and Baxter10 reported that 80% of patients un- dergoing revision resection noted substantial improvement; Patients typically report pain, paresthesias, or numbness on the however, less than 50% gained complete relief of symptoms. In anterolateral ankle and foot. Occasionally pain will radiate into the series of Johnson and colleagues,57 67% of patients experi- the thigh.67 Approximately 25% of patients recall a history of enced complete relief of symptoms, and 24% had no improve- trauma,67,109 which generally is an ankle sprain. A history of an- ment or even worsening of symptoms. Most of the procedures terior compartment fasciotomy is also clinically significant, as for these two series were performed through a plantar approach. noted previously. AAEM Course Painful Foot and Ankle 43

jacent web spaces.57 Examination of the tarsal tunnel, lower ex- In a small series of patients, Mann and Reynolds77 and Mann tremity, or the back may unmask areas of more proximal com- and Baxter76 observed that 81% of patients were asymptomatic 42 Surgical Management of Entrapment Neuropathies in the Foot, Including Indications and Outcomes AAEM Course pression contributing to interdigital symptoms. and 18% were either marginally or not improved after revision FOOT AND ANKLE NERVEsurgery DISORDERS through a dorsal approach. mal to the intermetatarsal ligament to ensure that all plantar nerves, or bilateral nerves yields less favorable results. Transection Diagnostic Studies The usual cause of Joplin’s neuroma is entrapment in scar tissue nerve branches are included in the resection.3,128 Other authors of the intermetatarsal ligament without neurectomy has been re- following bunion surgery. Most bunion procedures require 27,30,40 plication of the medial joint capsule, including the abductor have described a plantar approach through either longitudinal ported to yield approximately 80-85% satisfactory results. Plain radiographs should be obtained to ensure that no bony ab- SUPERFICIAL PERONEAL NERVE ENTRAPMENT hallucis tendon, which is located adjacent to the medial plantar incisions between the metatarsal heads or transverse incisions Additional study of patient selection factors and results with this normalities are present that may be responsible for continued proximal to the metatarsal heads.11,60,90,99 Plantar approaches technique are warranted. nerve as it courses to the hallux. Any surgical procedure on the nerve compression. Other imaging studies such as MRI or ul- medialOverview/Anatomy sesamoid, such as fracture repair or sesamoid removal, also may result in a painful scar if performed under or distal to the trasound may be suggestive of nerve pathology, but scar tissue puts the medial plantar nerve to the hallux at risk for developing metatarsal heads and longitudinal plantar incisions frequently from the previous surgical procedure may obscure interpreta- nerveEntrapment entrapment. of the superficial peroneal nerve (SPN) is not create fat pad atrophy and chronic metatarsalgia due to scar hy- RECURRENT INTERDIGITAL NEURALGIA tion. A repeat diagnostic anesthetic block in the affected web common.22,74,80,119 Although it may occur idiopathically, this 99 perkeratosis. Richardson and colleagues reported favorable on space may be useful in identifying residual or recurrent distal Individualsclinical entity can isalso typically develop associated a Joplin’s withneuroma ankle without instability, having65,74 the plantar approach, but observed that wound drainage, plantar Overview/Etiology nerve pathology. Occasionally, evaluation of a neuropathy is in- surgerydirect traumain the area (with adjacent associated to the ganglion),nerve. Repetitive67,116 fibular stress fracture, injuries,9 keratosis, and scar tenderness were the most common complica- dicated, including blood tests, nerve studies, or MRIs of the suchexertional as is seen compartment in ballet dancers syndrome or track and (and field previous athletes, fas-can tions. A transverse incision proximal to the metatarsal heads Recurrent or persistent interdigital neuralgia is often the results spine. alsociotomy), lead to119,120 a Joplin’smuscle neuroma. herniation, Also,39,80 injurieslower extremityto the sesamoid, edema, allows for adequate exposure for nerve resection and avoids in- of an incorrect diagnosis rather than a true recurrence.57,76 A suchand as (rarely) osteonecrosis, mass effects that such result as in tumors. hypertrophy5 Probably or irregularity the most terference with the metatarsal heads during weightbearing. more proximal nerve compromise may contribute to the inter- Management inmeaningful the shape ofassociation the sesamoid, is that can of leadchronic to pressure ankle sprains on the and medial per- digital symptoms, either completely or as part of a double-crush plantar nerve to the hallux. 108 AAEM Course Painful Foot andsistent Ankle postinjury anterolateral ankle pain. 43 Several authors have recommended dorsal approach for trans- phenomenon; therefore more proximal areas of compression Results of management of recurrent or persistent interdigital 27,30,40 Treatment of a Joplin’s neuroma begins with decompressing the verse metatarsal ligament transection without neurectomy, should be identified. Occasionally, the incorrect web space may 57 77 jacentneuralgia web are spaces. typicallyExamination less successful of the than tarsal those tunnel, for primary lower ex- in- affectedInAnatomic a small area seriesconsiderations with of properpatients, paddingare Mann important. inand the Reynolds After shoes. branching If thisand failsMann from to treating the condition as an entrapment syndrome. Although be identified on initial examination, and the surgical procedure tremity,terdigital or neuralgia. the back10,57 mayN unmaskonoperative areas management of more proximal should com-be re- andthe Baxter common76 observed peroneal that nerve, 81% the of patients SPN usually were asymptomatic courses in the 56,57 relieve the symptoms after 4 weeks, injection of the nerve with this procedure avoids potential recurrent or refractory plantar performed on the incorrect interdigital nerve. If the pathol- pressionpeated, contributing as for a to primary interdigital interdigital symptoms. neuralgia with aandlateral corticosteroid 18% compartment were either can be marginallyof attempted.the leg. Itor Ifpassesnot this improved throughtreatment aftera alsodeep revision fails fascial to neuroma formation because neurectomy is not performed, there ogy truly was at the web space, then persistent or recurrent accommodative shoe wear, metatarsal supports, NSAIDS, and decreasesurgerytunnel throughapproximately the pain, a dorsal then 8-12 surgicalapproach. cm above decompression the lateral malleolus, of the Joplin’s after is concern that several clinicians have observed reconstitution of symptoms may be secondary to inadequate proximal nerve re- possiblyDiagnostic a cortisone Studies injection.10,77 Physical therapy desensitiza- neuromawhich the is nerveperformed. divides further into medial and intermediate cu- the transverse intermetatarsal ligament.77,128 However, long-term section with neuroma formation in a weightbearing portion of tion modalities may prove beneficial. taneous branches.1,119 The medial branch supplies sensation to 3,10,56,57,76 follow-up with this technique suggests that this ligament recon- the forefoot or inadequate intermetatarsal ligament Plain radiographs should be obtained to ensure that no bony ab- SUPERFICIALthe dorsomedial PERONEAL aspect of NERVEthe ankle ENTRAPMENT and foot, whereas the inter- 40 77 76 stitution is probably not clinically significant. release. Mann and Reynolds and Mann and Baxter have also normalitiesAs with primary are present interdigital that mayneuralgia be responsible that has failed for continuednonopera- mediate branch is responsible for sensation over the dorsocentral observed an accessory branch or traumatic neuroma that is fre- nervetive management, compression. the Other approach imaging may studies be dorsal such14,77 as orMRI plantar or ul-10,57 Overview/Anatomyaspect of the ankle and foot.106 The fibrous tunnel is a site of po- Postoperatively, a patient is placed in a postoperative shoe and quently missed at the time of primary nerve resection and which trasoundin revision may surgery. be suggestive Proponents of nerve of thepathology, dorsal approachbut scar tissue cite a tential nerve entrapment, as is muscle herniation through the may bear weight on the heel. At 2 weeks, sutures are removed. remains under the metatarsal head after resection of the remain- fromconcern the for previous plantar surgical wound procedure complications; may 77 obscurethose preferring interpreta- a Efascialntrapment aperture of where the superficial the nerve leaves peroneal the compartment. nerve (SPN) 119 is S notuch Patients may progress with activity as tolerated but are instructed der of the nerve. tion.plantar A repeatincision diagnostic state that anestheticthe plantar blockapproach in the allows affected for greater web common.herniation22,74,80,119 may onlyAlthough occur in itthe may dynamic occur state idiopathically, and be part thisof a that there may be flares of nerve symptoms for several months. spaceproximal may resection be useful of inthe identifying nerve and avoids residual dorsal or recurrent scar tissue distal from clinicallocalized entity “anterior is typically exertional associated compartment with ankle syndrome.” instability, Ankle65,74 Surgical excision of an interdigital nerve obviously results in Evaluation nervethe previous pathology. surgery. Occasionally,10,57 A transverse evaluation plantar of a incision neuropathy can also is in- be directinversion trauma instability (with associatedmay produce ganglion), a traction67,116 injuryfibular to fracture,the inter-9 numbness between the affected toes; it is advisable to inform pa- dicated,used, as includingin primary blood interdigital tests, neuroma nerve studies, resection. or MRIs of the exertionalmediate cutaneous compartment branch, especially syndrome if the (and nerve previous is trapped fas- at tients of this preoperatively. History spine. ciotomy),the site of119,120 exit frommuscle the herniation,deep fascia.39,80 Therefore,lower extremity SPN entrapment edema, Results andshould (rarely) be considered mass effects in patients such as with tumors. chronic5 Probably pain after the mostankle Results Because recurrence or persistence of interdigital neuralgia after Management meaningfulsprain. Occasionally, association SPN is that neuralgia of chronic occurs ankle after sprains anterior and com-per- surgical resection is frequently due to misdiagnosis, evaluation as Typically, nonoperative management of recurrent or persistent sistentpartment postinjury fasciotomy anterolateral due to reorientation ankle pain. 108of the fascia, the nerve, 10,76 It has been estimated that only 20% of patients experience com- described for virgin interdigital neuralgia should be repeated. Rinterdigitalesults of management neuralgia/neuroma of recurrent is palliative. or persistent10,57 M interdigitalann and and the fibrous tunnel.119 plete resolution of symptoms of interdigital neuralgia with non- To administer appropriate management, it is essential to localize neuralgiaReynolds are77 estimated typically successfulless successful nonoperative than those management for primary to in- be Anatomic considerations are important. After branching from 46 operative measures alone. Results of corticosteroid injection symptoms, and a review of preoperative symptoms is often terdigitalbetween neuralgia.10 and 20%.10,57 N Resultsonoperative of revision management interdigital should nerve be re-re- theEvaluation common peroneal nerve, the SPN usually courses in the 76 suggest that although most patients gain temporary relief of helpful. History should include whether or not the patient had peated,section are as less for predictable a primary than interdigital for primary neuralgia procedure, with with lateral compartment of the leg. It passes through a deep fascial symptoms, symptoms are rarely eliminated completely. a symptom-free interval with weightbearing after primary nerve accommodativepatient dissatisfaction shoe wear, with resultsmetatarsal after supports, reoperation NSAIDS, approaching and tunnelHistory approximately 8-12 cm above the lateral malleolus, after 47 Greenfield and colleagues suggested that, in a series of steroid resection. Any associated symptoms, such as radiation of pain possibly40%.76,77 a B cortisoneeskin and injection. Baxter10 10,77reportedPhysical that therapy80% of desensitiza-patients un- which the nerve divides further into medial and intermediate cu- 10 injections for suspected interdigital neuralgia, only 30% of pa- from the ankle, leg, or back, should be noted. tiondergoing modalities revision may resectionprove beneficial. noted substantial improvement; taneousPatients branches. typically 1,119reportThe pain, medial paresthesias, branch supplies or numbness sensation on theto tients had substantial relief over a 2-year period. More recently, however, less than 50% gained complete relief of symptoms. In theanterolateral dorsomedial ankle aspect and of foot. the Occasionallyankle and foot, pain whereas will radiate the inter- into 96 Rasmussen and colleagues noted that although most patients Physical Examination Asthe with series primary of Johnson interdigital and colleagues, neuralgia 57that67% has of failed patients nonopera- experi- mediatethe thigh. branch67 Approximately is responsible 25% for sensation of patients over recall the dorsocentral a history of with third web space neuralgia had relief of symptoms with a tiveenced management, complete relief the approachof symptoms, may beand dorsal 24%14,77 hador no plantar improve-10,57 aspecttrauma, of67,109 the anklewhich and generally foot.106 isThe an anklefibrous sprain. tunnel A is history a site of of po- an- single steroid injection, most were still symptomatic. Of the 51 Physical examination of the forefoot may reveal a localized area AAEM Course Painful Foot andinment Ankle revision or even surgery. worsening Proponents of symptoms. of the dorsalMost of approach the procedures cite 43 a tentialterior compartmentnerve entrapment, fasciotomy as is muscle is also herniation clinically significant, through the as feet in the study, 50% underwent subsequent surgical resection of tenderness and a positive Tinel’s sign, suggestive of a stump concernfor these for two plantar series werewound performed complications; through77 athose plantar preferring approach. a fascialnoted aperture previously. where the nerve leaves the compartment.119 Such 3,57,128 with 96% success; the other 50% remained symptomatic. neuroma. jacentPalpation web spaces. of the57 metatarsalExamination heads of maythe tarsal be sugges- tunnel, lower ex- plantarIn a small incision series state of thatpatients, the plantar Mann approachand Reynolds allows77 forand greater Mann herniation may only occur in the dynamic state and be part of a tive of an accessorytremity, or nerve the branchback may (as unmask described areas by of Mann more and proximal com- proximaland Baxter resection76 observed of the that nerve 81% and of avoids patients dorsal were scar asymptomatic tissue from localized “anterior exertional compartment syndrome.” Ankle 77 76 Reports of common digital nerve resection for failed nonopera- Reynolds andpression Mann contributing and Baxter to )interdigital or other bonysymptoms. pathology theand previous 18% were surgery. either10,57 marginallyA transverse or plantarnot improved incision after can revisionalso be inversion instability may produce a traction injury to the inter- tive management of interdigital neuralgia suggests satisfactory that may be creating nerve impingement. Other forefoot pathol- used,surgery as inthrough primary a dorsalinterdigital approach. neuroma resection. mediate cutaneous branch, especially if the nerve is trapped at 38,77,96 relief of symptoms in 80-96% of patients. Results appear ogy may be responsibleDiagnostic for theStudies pain, and thus other sources of the site of exit from the deep fascia. Therefore, SPN entrapment to be best for isolated third web space neuralgia. Resection of iso- symptoms should be identified, such as MTP joint synovitis or RJoplin’sesults neuroma (medial plantar proper digital nerve syndrome) should be considered in patients with chronic pain after ankle lated common digital nerves other than the third, multiple metatarsalgia.P lainOccasionally, radiographs interdigital should be neuralgia obtained is to found ensure in that ad- no bony ab- isSUPERFICIAL caused by entrapment PERONEAL of NERVEthe medial ENTRAPMENT plantar nerve to the hallux sprain. Occasionally, SPN neuralgia occurs after anterior com- normalities are present that may be responsible for continued Tadjacentypically, to nonoperative the medial sesamoid. management The hallmarkof recurrent of this or conditionpersistent is partment fasciotomy due to reorientation of the fascia, the nerve, nerve compression. Other imaging studies such as MRI or ul- interdigitalpainOverview/Anatomy and a positive neuralgia/neuroma Tinel’s sign adjacent is palliative. to the10,57 medialMann sesamoid. and and the fibrous tunnel.119 trasound may be suggestive of nerve pathology, but scar tissue Reynolds77 estimated successful nonoperative management to be 43 from the previous surgical procedure may obscure interpreta- betweenEntrapment 10 and of 20%. the superficial Results of peronealrevision interdigital nerve (SPN) nerve is re- not Evaluation tion. A repeat diagnostic anesthetic block in the affected web sectioncommon. are22,74,80,119 less predictableAlthough than it may for primary occur idiopathically, procedure, with this space may be useful in identifying residual or recurrent distal patientclinical dissatisfaction entity is typically with results associated after withreoperation ankle instability,approaching65,74 History nerve pathology. Occasionally, evaluation of a neuropathy is in- 40%.direct76,77 traumaBeskin (with and Baxter associated10 reported ganglion), that67,116 80%fibular of patients fracture, un- 9 dicated, including blood tests, nerve studies, or MRIs of the dergoingexertional revision compartment resection notedsyndrome substantial (and improvement; previous fas- Patients typically report pain, paresthesias, or numbness on the spine. however,ciotomy), less119,120 thanmuscle 50% gained herniation, complete39,80 lower relief extremityof symptoms. edema, In anterolateral ankle and foot. Occasionally pain will radiate into theand series (rarely) of Johnson mass effects and colleagues, such as tumors.57 67%5 ofPr obablypatients the experi- most the thigh.67 Approximately 25% of patients recall a history of Management encedmeaningful complete association relief of issymptoms, that of chronic and 24% ankle had sprains no improve- and per- trauma,67,109 which generally is an ankle sprain. A history of an- mentsistent or postinjury even worsening anterolateral of symptoms. ankle pain. Most108 of the procedures terior compartment fasciotomy is also clinically significant, as Results of management of recurrent or persistent interdigital for these two series were performed through a plantar approach. noted previously. neuralgia are typically less successful than those for primary in- Anatomic considerations are important. After branching from terdigital neuralgia.10,57 Nonoperative management should be re- the common peroneal nerve, the SPN usually courses in the peated, as for a primary interdigital neuralgia with lateral compartment of the leg. It passes through a deep fascial accommodative shoe wear, metatarsal supports, NSAIDS, and tunnel approximately 8-12 cm above the lateral malleolus, after possibly a cortisone injection.10,77 Physical therapy desensitiza- which the nerve divides further into medial and intermediate cu- tion modalities may prove beneficial. taneous branches.1,119 The medial branch supplies sensation to the dorsomedial aspect of the ankle and foot, whereas the inter- As with primary interdigital neuralgia that has failed nonopera- mediate branch is responsible for sensation over the dorsocentral tive management, the approach may be dorsal14,77 or plantar10,57 aspect of the ankle and foot.106 The fibrous tunnel is a site of po- in revision surgery. Proponents of the dorsal approach cite a tential nerve entrapment, as is muscle herniation through the concern for plantar wound complications;77 those preferring a fascial aperture where the nerve leaves the compartment.119 Such plantar incision state that the plantar approach allows for greater herniation may only occur in the dynamic state and be part of a proximal resection of the nerve and avoids dorsal scar tissue from localized “anterior exertional compartment syndrome.” Ankle the previous surgery.10,57 A transverse plantar incision can also be inversion instability may produce a traction injury to the inter- used, as in primary interdigital neuroma resection. mediate cutaneous branch, especially if the nerve is trapped at the site of exit from the deep fascia. Therefore, SPN entrapment Results should be considered in patients with chronic pain after ankle sprain. Occasionally, SPN neuralgia occurs after anterior com- Typically, nonoperative management of recurrent or persistent partment fasciotomy due to reorientation of the fascia, the nerve, interdigital neuralgia/neuroma is palliative.10,57 Mann and and the fibrous tunnel.119 Reynolds77 estimated successful nonoperative management to be between 10 and 20%. Results of revision interdigital nerve re- Evaluation section are less predictable than for primary procedure, with patient dissatisfaction with results after reoperation approaching History 40%.76,77 Beskin and Baxter10 reported that 80% of patients un- dergoing revision resection noted substantial improvement; Patients typically report pain, paresthesias, or numbness on the however, less than 50% gained complete relief of symptoms. In anterolateral ankle and foot. Occasionally pain will radiate into the series of Johnson and colleagues,57 67% of patients experi- the thigh.67 Approximately 25% of patients recall a history of enced complete relief of symptoms, and 24% had no improve- trauma,67,109 which generally is an ankle sprain. A history of an- ment or even worsening of symptoms. Most of the procedures terior compartment fasciotomy is also clinically significant, as for these two series were performed through a plantar approach. noted previously. 44 Surgical Management of Entrapment Neuropathies in the Foot, Including Indications and Outcomes AAEM Course

Physical Examination Operative

AAEM Course Painful Foot and Ankle 43 As with any neurologic evaluation of the lower extremity, more In isolated nerve pathology, operative intervention is directed at proximal areas of nerve compromise should be identified, and nerve decompression, which usually involves release of the nerve jacent web spaces.57 Examination of the tarsal tunnel, lower ex- In a small series of patients, Mann and Reynolds77 and Mann examination should rule out radiculopathy and entrapment of at the fibrous tunnel.65,74,80,119 A more extensive compartment tremity, or the back may unmask areas of more proximal com- and Baxter76 observed that 81% of patients were asymptomatic the sciatic and common peroneal nerves. Ankle instability release can be performed to eliminate muscle herniation on the pression contributing to interdigital symptoms. and 18% were either marginally or not improved after revision should be documented. Palpation of the SPN may identify a SPN.119 In the rare cases in which previous anterior compart- surgery through a dorsal approach. specific site of nerve irritation, muscle herniation, fascial defect, ment release has resulted in SPN, revision of the fascial release Diagnostic Studies and/or bony prominences.109 Palpation of the nerve may and lateral fascial release may be required.119 Any mass effect of produce paresthesias in the distribution of the SPN. Usually, the exostoses should also be removed. When nerve compromise is Plain radiographs should be obtained to ensure that no bony ab- SUPERFICIAL PERONEAL NERVE ENTRAPMENT problem can be localized to the area where the nerve exits from associated with ankle instability, then nerve decompression is normalities are present that may be responsible for continued the fascia.109,119 Styf118 described three provocative tests to aid in combined with lateral ankle ligament reconstruction.9 nerve compression. Other imaging studies such as MRI or ul- Overview/Anatomy diagnosis of SPN entrapment once the site of nerve irritation is trasound may be suggestive of nerve pathology, but scar tissue identified. The first test involves palpation of the nerve while the Results from the previous surgical procedure may obscure interpreta- Entrapment of the superficial peroneal nerve (SPN) is not patient actively dorsiflexes and everts the ankle; the two other tion. A repeat diagnostic anesthetic block in the affected web common.22,74,80,119 Although it may occur idiopathically, this tests involve plantarflexion and inversion with and without pal- Results of nonoperative management are not extensively ad- space may be useful in identifying residual or recurrent distal clinical entity is typically associated with ankle instability,65,74 pation at the site of nerve irritation. Findings from these tests dressed in the literature. It has been suggested that relief of symp- nerve pathology. Occasionally, evaluation of a neuropathy is in- direct trauma (with associated ganglion),67,116 fibular fracture,9 may be difficult to distinguish from mechanical symptoms in toms of long-standing SPN entrapment by nonoperative means dicated, including blood tests, nerve studies, or MRIs of the exertional compartment syndrome (and previous fas- patients with associated chronic ankle instability. Some patients is typically inadequate.108,109 However, it can be inferred that if spine. ciotomy),119,120 muscle herniation,39,80 lower extremity edema, may have decreased sensation distal to the site of maximum irri- SPN symptoms are secondary to dynamic causes, such as and (rarely) mass effects such as tumors.5 Probably the most tation. chronic ankle instability, then stabilization will result in im- Management meaningful association is that of chronic ankle sprains and per- provement of symptoms. sistent postinjury anterolateral ankle pain.108 Diagnostic Studies Results of management of recurrent or persistent interdigital The largest series of SPN decompression suggests that improve- neuralgia are typically less successful than those for primary in- Anatomic considerations are important. After branching from Plain radiographs may reveal fracture fragments or bony promi- ment of symptoms can be anticipated in 75% of cases, but it terdigital neuralgia.10,57 Nonoperative management should be re- the common peroneal nerve, the SPN usually courses in the nences that may be responsible for symptoms.119 warned that results are less predictable in athletes.119 Case reports peated, as for a primary interdigital neuralgia with lateral compartment of the leg. It passes through a deep fascial Electrodiagnostic studies may be useful in confirming areas of of SPN release have demonstrated effective relief of symp- accommodative shoe wear, metatarsal supports, NSAIDS, and tunnel approximately 8-12 cm above the lateral malleolus, after SPN compromise suggested on clinical examination and are es- toms.65,74,80 possibly a cortisone injection.10,77 Physical therapy desensitiza- which the nerve divides further into medial and intermediate cu- pecially useful in diagnosing more proximal nerve compromise tion modalities may prove beneficial. taneous branches.1,119 The medial branch supplies sensation to or peripheral neuropathy.119 Diagnostic anesthetic blocks may the dorsomedial aspect of the ankle and foot, whereas the inter- also confirm the diagnosis of SPN neuralgia.9,65,108 Should DEEP PERONEAL NERVE ENTRAPMENT (“ANTERIOR TARSAL As with primary interdigital neuralgia that has failed nonopera- mediate branch is responsible for sensation over the dorsocentral history and physical examination suggest exertional compart- TUNNEL SYNDROME”) tive management, the approach may be dorsal14,77 or plantar10,57 aspect of the ankle and foot.106 The fibrous tunnel is a site of po- ment syndrome, compartment pressure measurements are per- in revision surgery. Proponents of the dorsal approach cite a tential nerve entrapment, as is muscle herniation through the formed.108,119 Overview/Etiology/Anatomy concern for plantar wound complications;77 those preferring a fascial aperture where the nerve leaves the compartment.119 Such plantar incision state that the plantar approach allows for greater herniation may only occur in the dynamic state and be part of a Management Deep peroneal nerve (DPN) entrapment was initially described proximal resection of the nerve and avoids dorsal scar tissue from localized “anterior exertional compartment syndrome.” Ankle by Kopell and Thompson66 in 1960 and was designated an “an- the previous surgery.10,57 A transverse plantar incision can also be inversion instability may produce a traction injury to the inter- Nonoperative terior tarsal tunnel syndrome” by Marinacci78 in 1968. The used, as in primary interdigital neuroma resection. mediate cutaneous branch, especially if the nerve is trapped at DPN branches from the common peroneal nerve and courses the site of exit from the deep fascia. Therefore, SPN entrapment Nonoperative management is usually aimed at eliminating po- between the extensor hallucis longus and the extensor digitorum Results should be considered in patients with chronic pain after ankle tential traction on the entrapped SPN with modalities typically longus just proximal to the ankle. Approximately 1 cm above the sprain. Occasionally, SPN neuralgia occurs after anterior com- used in the treatment of ankle instability/sprains.9,108 Physical ankle joint, the nerve divides into a motor branch to the exten- Typically, nonoperative management of recurrent or persistent partment fasciotomy due to reorientation of the fascia, the nerve, therapy to strengthen the peroneal musculature, ankle bracing, sor digitorum brevis (EDB) and a sensory branch that continues interdigital neuralgia/neuroma is palliative.10,57 Mann and and the fibrous tunnel.119 and lateral shoe wedges have been described. An ankle/foot or- to the first web space. As this sensory branch crosses the ankle Reynolds77 estimated successful nonoperative management to be Surgical Management of Entrapmentthosis N europathiesin neutral worn in at the night Foot may decrease SPN symptoms by and the dorsum of the foot, there are several sites of potential between 10 and 20%. Results of revision interdigital nerve re- Evaluation decreasing the stretch on the nerve. However, these modalities compression. Because the motor branch to the EDB is proximal section are less predictable than for primary procedure, with need to be used cautiously. Vigorous strengthening of the per- to these sites of compression, the findings are typically related patient dissatisfaction with results after reoperation approaching History oneal musculature may further irritate the SPN at the fibrous purely to the sensory branch.26 Krause and colleagues68 described 40%.76,77 Beskin and Baxter10 reported that 80% of patients un- tunnel, and ankle braces may create external compression of the a “partial anterior tarsal tunnel syndrome” in which only the dergoing revision resection noted substantial improvement; Patients typically report pain, paresthesias, or numbness on the 44 Surgical Management of Entrapment Neuropathies innerve the Foot, fibers. Including Vitamin Indications B6, NSAIDs,and Outcomes TCAs, and antiepilepticAAEM Course motor or sensory component was involved. The most frequently however, less than 50% gained complete relief of symptoms. In anterolateral ankle and foot. Occasionally pain will radiate into medications may reduce symptoms. Corticosteroid injections at described site of entrapment is between the inferior edge of the 57 67 the series of Johnson and colleagues, 67% of patients experi- the Physicalthigh. A Examinationpproximately 25% of patients recall a history of the siteOperative of nerve compromise may also diminish symptoms. extensor retinaculum and the talus and navicular, where these enced complete relief of symptoms, and 24% had no improve- trauma,67,109 which generally is an ankle sprain. A history of an- ment or even worsening of symptoms. Most of the procedures terior compartment fasciotomy is also clinically significant, as As44 with any neurologicSurgical evaluation Management of the lower of Entrapment extremity, Neuropathies more inIn the isolated Foot, Including nerve pathology, Indications operative and Outcomes intervention isAAEM directed Course at for these two series were performed through a plantar approach. proximalnoted previously. areas of nerve compromise should be identified, and nerve decompression, which usually involves release of the nerve examinationPhysical should Examination rule out radiculopathy and entrapment of at theOperative fibrous tunnel.65,74,80,119 A more extensive compartment the sciatic and common peroneal nerves. Ankle instability release can be performed to eliminate muscle herniation on the shouldAs with be any documented. neurologic evaluation Palpation of the lower SPN mayextremity, identify more a SPN.In isolated119 In thenerve rare pathology, cases in operativewhich previous intervention anterior is directedcompart- at specificproximal site areas of nerve of nerve irritation, compromise muscle herniation,should be identified, fascial defect, and mentnerve release decompression, has resulted which in SPN, usually revision involves of releasethe fascial of the release nerve and/orexamination bony should prominences. rule out109 radiculopathyPalpation of and the entrapment nerve may of andat thelateral fibrous fascial tunnel. release65,74,80,119 may beA required. more extensive119 Any mass compartment effect of producethe sciatic paresthesias and common in the distribution peroneal nerves.of the SPN. Ankle Usually, instability the exostosesrelease can should be performed also be removed. to eliminate When muscle nerve herniation compromise on theis problemshould becan documented. be localized to Palpation the area ofwhere the the SPN nerve may exits identify from a associatedSPN.119 In with the anklerare cases instability, in which then previous nerve decompressionanterior compart- is thespecific fascia. site109,119 of nerveStyf118 irritation,described musclethree provocative herniation, tests fascial to aiddefect, in combinedment release with has lateral resulted ankle in ligament SPN, revision reconstruction. of the fascial9 release diagnosisand/or bonyof SPN prominences. entrapment109 oncePalpa thetion site of of nerve the irritation nerve may is and lateral fascial release may be required.119 Any mass effect of identified.produce paresthesias The first test in involvesthe distribution palpation of of the the SPN. nerve Usually, while the the Rexostosesesults should also be removed. When nerve compromise is patientproblem actively can be dorsiflexes localized toand the everts area wherethe ankle; the nerve the two exits other from associated with ankle instability, then nerve decompression is teststhe fascia.involve109,119 plantarflexionStyf118 described and inversion three provocative with and testswithout to aid pal- in Rcombinedesults of nonoperativewith lateral ankle management ligament reconstruction. are not extensively9 ad- pationdiagnosis at theof SPNsite ofentrapment nerve irritation. once the Findings site of nervefrom irritationthese tests is dressed in the literature. It has been suggested that relief of symp- mayidentified. be difficult The first to distinguishtest involves from palpation mechanical of the nerve symptoms while the in tomsResults of long-standing SPN entrapment by nonoperative means patientspatient withactively associated dorsiflexes chronic and ankleeverts instability.the ankle; Somethe two patients other is typically inadequate.108,109 However, it can be inferred that if maytests have involve decreased plantarflexion sensation and distal inversion to the sitewith of and maximum without irri- pal- SPNResults symptoms of nonoperative are secondary management to dynamic are not causes, extensively such ad- as tation.pation at the site of nerve irritation. Findings from these tests chronicdressed in ankle the literature. instability, It thenhas been stabilization suggested willthat resultrelief of in symp- im- may be difficult to distinguish from mechanical symptoms in provementtoms of long-standing of symptoms. SPN entrapment by nonoperative means patientsDiagnostic with associated Studies chronic ankle instability. Some patients is typically inadequate.108,109 However, it can be inferred that if may have decreased sensation distal to the site of maximum irri- TheSPN largest symptoms series of are SPN secondary decompression to dynamic suggests causes, that improve- such as Ptation.lain radiographs may reveal fracture fragments or bony promi- mentchronic of symptoms ankle instability, can be thenanticipated stabilization in 75% will of resultcases, inbut im- it nences that may be responsible for symptoms.119 warnedprovement that ofresults symptoms. are less predictable in athletes.119 Case reports ElectrodiagnosticDiagnostic Studiesstudies may be useful in confirming areas of of SPN release have demonstrated effective relief of symp- SPN compromise suggested on clinical examination and are es- toms.The 65,74,80largest series of SPN decompression suggests that improve- peciallyPlain radiographs useful in diagnosing may reveal more fracture proximal fragments nerve or compromisebony promi- ment of symptoms can be anticipated in 75% of cases, but it ornences peripheral that neuropathy. may be119 D responsibleiagnostic anesthetic for symptoms. blocks may119 warned that results are less predictable in athletes.119 Case reports alsoElectrodiagnostic confirm the studies diagnosis may of be SPN useful neuralgia. in confirming9,65,108 Sareashould of DEEPof SPN PERONEAL release haveNERVE demonstrated ENTRAPMENT effective (“ANTERIOR relief TARSAL of symp- historySPN compromise and physical suggested examination on clinical suggest examination exertional and compart- are es- TUNNELtoms.65,74,80 SYNDROME”) mentpecially syndrome, useful in compartment diagnosing more pressure proximal measurements nerve compromise are per- formed.or peripheral108,119 neuropathy.119 Diagnostic anesthetic blocks may Overview/Etiology/Anatomy also confirm the diagnosis of SPN neuralgia.9,65,108 Should DEEP PERONEAL NERVE ENTRAPMENT (“ANTERIOR TARSAL Managementhistory and physical examination suggest exertional compart- DTUNNELeep peroneal SYNDROME”) nerve (DPN) entrapment was initially described ment syndrome, compartment pressure measurements are per- by Kopell and Thompson66 in 1960 and was designated an “an- formed.Nonoperative108,119 teriorOverview/Etiology/Anatomy tarsal tunnel syndrome” by Marinacci78 in 1968. The DPN branches from the common peroneal nerve and courses NManagementonoperative management is usually aimed at eliminating po- betweenDeep peroneal the extensor nerve hallucis (DPN) longus entrapment and the was extensor initially digitorum described tential traction on the entrapped SPN with modalities typically longusby Kopell just andproximal Thompson66 to the ankle. in 1960 Approximately and was designated 1 cm above an “an-the used Nonoperative in the treatment of ankle instability/sprains.9,108 Physical ankleterior joint, tarsal the tunnel nerve syndrome”divides into bya motor Marinacci branch78 in to 1968.the exten- The therapy to strengthen the peroneal musculature, ankle bracing, sorDPN digitorum branches brevis from (EDB) the common and a sensory peroneal branch nerve that and continues courses andNonoperative lateral shoe management wedges have isbeen usually described. aimed Anat eliminating ankle/foot or-po- tobetween the first the web extensor space. hallucis As this longussensory and branch the extensor crosses thedigitorum ankle thosistential in traction neutral onworn the at entrapped night may SPN decrease with SPNmodalities symptoms typically by andlongus the justdorsum proximal of the to thefoot, ankle. there Approximately are several sites 1 cmof potentialabove the decreasingused in the the treatment stretch on of the ankle nerve. instability/sprains. However, these9,108 modalitiesPhysical compression.ankle joint, the Because nerve thedivides motor into branch a motor to the branch EDB to is theproximal exten- needtherapy to beto usedstrengthen cautiously. the peroneal Vigorous musculature, strengthening ankle of thebracing, per- tosor these digitorum sites of brevis compression, (EDB) and the a sensoryfindings branch are typically that continues related onealand lateralmusculature shoe wedges may furtherhave been irritate described. the SPN An atankle/foot the fibrous or- purelyto the to first the web sensory space. branch. As this26 Krause sensory and branch colleagues crosses68 described the ankle tunnel,thosis inand neutral ankle wornbraces at may night create may externaldecrease compression SPN symptoms of the by aand “partial the dorsum anterior of tarsal the foot, tunnel there syndrome” are several in sites which of onlypotential the nervedecreasing fibers. the Vitamin stretch on B6, the NSAIDs, nerve. However, TCAs, and these antiepileptic modalities motorcompression. or sensory Because component the motor was branchinvolved. to Thethe EDBmost isfrequently proximal medications44need to be usedmay reducecautiously. symptoms. Vigorous Corticosteroid strengthening injections of the per- at describedto these sitessite ofof entrapmentcompression, is betweenthe findings the inferiorare typically edge ofrelated the theoneal site musculature of nerve compromise may further may irritate also diminish the SPN symptoms. at the fibrous extensorpurely to retinaculum the sensory branch.and the26 talusKrause and and navicular, colleagues where68 described these tunnel, and ankle braces may create external compression of the a “partial anterior tarsal tunnel syndrome” in which only the nerve fibers. Vitamin B6, NSAIDs, TCAs, and antiepileptic motor or sensory component was involved. The most frequently medications may reduce symptoms. Corticosteroid injections at described site of entrapment is between the inferior edge of the the site of nerve compromise may also diminish symptoms. extensor retinaculum and the talus and navicular, where these 44 Surgical Management of Entrapment Neuropathies in the Foot, Including Indications and Outcomes AAEM Course

Physical Examination Operative

As with any neurologic evaluation of the lower extremity, more In isolated nerve pathology, operative intervention is directed at proximal areas of nerve compromise should be identified, and nerve decompression, which usually involves release of the nerve examination should rule out radiculopathy and entrapment of at the fibrous tunnel.65,74,80,119 A more extensive compartment the sciatic and common peroneal nerves. Ankle instability release can be performed to eliminate muscle herniation on the should be documented. Palpation of the SPN may identify a SPN.119 In the rare cases in which previous anterior compart- specific site of nerve irritation, muscle herniation, fascial defect, ment release has resulted in SPN, revision of the fascial release and/or bony prominences.109 Palpation of the nerve may and lateral fascial release may be required.119 Any mass effect of produce paresthesias in the distribution of the SPN. Usually, the exostoses should also be removed. When nerve compromise is problem can be localized to the area where the nerve exits from associated with ankle instability, then nerve decompression is the fascia.109,119 Styf118 described three provocative tests to aid in combined with lateral ankle ligament reconstruction.9 diagnosis of SPN entrapment once the site of nerve irritation is identified. The first test involves palpation of the nerve while the Results patient actively dorsiflexes and everts the ankle; the two other tests involve plantarflexion and inversion with and without pal- Results of nonoperative management are not extensively ad- pation at the site of nerve irritation. Findings from these tests dressed in the literature. It has been suggested that relief of symp- may be difficult to distinguish from mechanical symptoms in toms of long-standing SPN entrapment by nonoperative means patients with associated chronic ankle instability. Some patients is typically inadequate.108,109 However, it can be inferred that if may have decreased sensation distal to the site of maximum irri- SPN symptoms are secondary to dynamic causes, such as tation. chronic ankle instability, then stabilization will result in im- provement of symptoms. Diagnostic Studies The largest series of SPN decompression suggests that improve- Plain radiographs may reveal fracture fragments or bony promi- ment of symptoms can be anticipated in 75% of cases, but it nences that may be responsible for symptoms.119 warned that results are less predictable in athletes.119 Case reports Electrodiagnostic studies may be useful in confirming areas of of SPN release have demonstrated effective relief of symp- SPN compromise suggested on clinical examination and are es- toms.65,74,80 pecially useful in diagnosing more proximal nerve compromise or peripheral neuropathy.119 Diagnostic anesthetic blocks may also confirm the diagnosis of SPN neuralgia.9,65,108 Should DEEP PERONEAL NERVE ENTRAPMENT (“ANTERIOR TARSAL history and physical examination suggest exertional compart- TUNNEL SYNDROME”) ment syndrome, compartment pressure measurements are per- formed.108,119 Overview/Etiology/Anatomy

Management Deep peroneal nerve (DPN) entrapment was initially described by Kopell and Thompson66 in 1960 and was designated an “an- Nonoperative terior tarsal tunnel syndrome” by Marinacci78 in 1968. The DPN branches from the common peroneal nerve and courses Nonoperative management is usually aimed at eliminating po- between the extensor hallucis longus and the extensor digitorum tential traction on the entrapped SPN with modalities typically longus just proximal to the ankle. Approximately 1 cm above the used in the treatment of ankle instability/sprains.9,108 Physical ankle joint, the nerve divides into a motor branch to the exten- therapy to strengthen the peroneal musculature, ankle bracing, sor digitorum brevis (EDB) and a sensory branch that continues and lateral shoe wedges have been described. An ankle/foot or- to the first web space. As this sensory branch crosses the ankle thosis in neutral worn at night may decrease SPN symptoms by and the dorsum of the foot, there are several sites of potential decreasing the stretch on the nerve. However, these modalities compression. Because the motor branch to the EDB is proximal need to be used cautiously. Vigorous strengthening of the per- to these sites of compression, the findings are typically related oneal musculature may further irritate the SPN at the fibrous purely to the sensory branch.26 Krause and colleagues68 described AAEM Course Painful Foot and Ankle 45 tunnel, and ankle braces may create external compression of the a “partial anterior tarsal tunnel syndrome” in FOOT which AND only ANKLE the NERVE DISORDERS nerve fibers. Vitamin B6, NSAIDs, TCAs, and antiepileptic structuresmotor or sensory create acomponent fibroosseous was “anterior involved. tarsal The most tunnel.” frequently42,78,109 and testing for ankle instability. If the history is consistent with medications may reduce symptoms. Corticosteroid injections at EAAEMdescribedntrapment Course site may of entrapmentalso occur at is the between superior the edge inferior of the edge extensorPainful of the Foot andan Ankle anterior compartment syndrome, then examination should45 the site of nerve compromise may also diminish symptoms. rextensoretinaculum, retinaculum at which and point the talus the EHLand navicular, tendon where crosses these the also be performed after exacerbation of symptoms on a tread- 42,78,109 DPN,structures12,78 and create also a fibroosseouswhere the nerve “anterior is crossed tarsal by tunnel.” the extensor mill,and testing with measurements for ankle instability. of compartment If the history pressures. is consistent with Ehallucisntrapment brevis may tendon. also occur67 Trauma at the and superior degenerative edge of changes the extensor have an anterior compartment syndrome, then examination should alsoretinaculum, been shown at to which contribute point to the deep EHL peroneal tendon neuralgia, crosses and the also Diagnosticbe performed Studies/Tests after exacerbation of symptoms on a tread- 12,78 dorsalDPN, osteophytesand also of where the foot the andnerve ankle is crossed may be by responsible the extensor for mill, with measurements of compartment pressures. 67 nervehallucis compression. brevis tendon.85,109 AlthoughTrauma and ankle degenerative instability ischanges more com-have Plain radiographs are useful in identifying exostoses or osteo- alsomonly been associated shown to withcontribute SPN to neuralgia, deep peroneal plantarflexion neuralgia, and phytesDiagnostic that mayStudies/Tests contribute to nerve compression. dorsalsupination osteophytes places the of theDPN foot under and maximumankle may tension,be responsible especially for Electrodiagnostic studies may reveal areas of distal entrapment 85,109 nervein the compression. presence of an underlyingAlthough ankletalonavicular instability osteophyte. is more com-12,108 butPlain are radiographs typically more are helpful useful inin identifying areas exostoses of more or osteo-prox- Emonlyxternal associated compression with or SPN certain neuralgia, aberrant plantarflexionpostures may con- and imalphytes nerve that compression may contribute or peripheral to nerve neuropathies. compression.26 tributesupination to deep places peroneal the DPN neuralgia. under Tightmaximum shoe weartension, and especiallyski boots EOlectrodiagnosticccasionally, nerve studies conduction may reveal studies areas assist of distal in distinguishing entrapment 12,108 havein the beenpresence implicated, of an underlying42,68,72 as hastalonavicular prolonged osteophyte. plantarflexion butbetween are typically distal and more proximal helpful DPN in identifying compression areas within of more the prox-ante- 26 duringExternal sleep, compression which places or the certain nerve aberrant under tension. postures Finally, may con-gan- imalrior tarsal nerve tunnel. compression A diagnostic ornerve peripheral block may neuropathies.confirm clinical glionstribute orto tumorsdeep peroneal rarely neuralgia.create pressure Tight on shoe the wear DPN and in ski the boots re- findingsOccasionally, and, asnerve noted conduction previously, studiescompartment assist in pressures distinguishing should 42,68,72 strictedhave been space implicated, of the anterior tarsalas has tunnel. prolonged109 plantarflexion bebetween measured distal if andanterior proximal compartment DPN compression syndrome within is suspected. the ante- during sleep, which places the nerve under tension. Finally, gan- rior tarsal tunnel. A diagnostic nerve block may confirm clinical glionsEvaluation or tumors rarely create pressure on the DPN in the re- Managementfindings and, as noted previously, compartment pressures should stricted space of the anterior tarsal tunnel.109 be measured if anterior compartment syndrome is suspected. History Nonoperative Evaluation Management Patients with deep peroneal neuralgia complain of dorsal foot Nonoperative measures include use of accommodative shoe wear pain Historythat may radiate to the first web space. As with other nerve that Nonoperative eliminates external compression on the dorsal ankle and symptoms of the foot and ankle, a history of low back pain foot and activity modification to avoid activities that exacerbate shouldPatients be with documented. deep peroneal If the neuralgia symptoms complain are aggravated of dorsal by foot ac- symptoms.Nonoperative As measures for SPN include neuralgia, use of ankle accommodative braces may shoe alleviate wear tivitypain that or exercise, may radiate then toconsideration the first web must space. be As given with to other exertional nerve nervethat eliminates pain related external to ankle compression instability but on may the potentially dorsal ankle worsen and compartmentsymptoms of syndrome. the foot and Symptoms ankle, a related history to oftight low shoe back wear pain or symptomsfoot and activity if external modification pressure isto created.avoid activities Vitamin that B6 ,exacerbate NSAIDs, particularshould be activitiesdocumented. (such If as the sit-ups symptoms with theare anterioraggravated aspect by ac-of symptoms.TCAs, and As antiepileptic for SPN neuralgia, medications ankle may braces reduce may symptoms, alleviate thetivity ankles or exercise, under athen metal consideration restraint) should must bebe noted.given toA exertionalhistory of nerveand corticosteroid pain related to injection ankle instability at the site but ofmay nerve potentially irritation worsen may footcompartment and ankle syndrome. trauma or Symptomschronic ankle related instability to tight is shoe also wearimpor- or symptomsalso be beneficial. if external pressure is created. Vitamin B6, NSAIDs, tant.particular activities (such as sit-ups with the anterior aspect of TCAs, and antiepileptic medications may reduce symptoms, the ankles under a metal restraint) should be noted. A history of and Operative corticosteroid injection at the site of nerve irritation may foot Physicaland ankle Examination trauma or chronic ankle instability is also impor- also be beneficial. tant. Surgical intervention involves decompression of the entrapped Palpation along the course of the DPN may identify an area of nerveOperative by release of the extensor retinaculum. If possible, a prox- maximumPhysical nerve Examination irritation, is usually in the area of the inferior imal portion of the retinaculum should be preserved to avoid extensor retinaculum.26 Palpation may also locate dorsal ankle “bowstringing”Surgical intervention of the involvesextensor decompressiontendons. Occasionally, of the entrappedthe exten- andPalpation foot osteophytesalong the course and rarelyof the a DPN ganglion may relatedidentify to an previous area of sornerve hallucis by release brevis of tendonthe extensor must retinaculum.be released. All If possible,osteophytes a prox- and traumamaximum or degenerativenerve irritation, change. is usually Sensation in the in areathe firstof the web inferior space exostosesimal portion should of thebe resectedretinaculum as well. should108 If beankle preserved instability to avoidis di- 26 mayextensor be diminished. retinaculum. AreasPalpation of more mayproximal also locatenerve compromisedorsal ankle agnosed“bowstringing” as a major of the contributing extensor tendons. factor to Occasionally, deep peroneal the neural- exten- shouldand foot be osteophytes ruled out with and examination rarely a ganglion of the relatedlower spine, to previous sciatic gia,sor hallucis then anklebrevis tendon ligament must reconstruction be released. All may osteophytes need to and be 108 nerve,trauma common or degenerative peroneal change. nerve. WeaknessSensation and/orin the firstatrophy web ofspace the considered.exostoses should Finally, be whenresected anterior as well. compartmentIf ankle instability syndrome is hasdi- EDBmay be muscle diminished. is suggestive Areas of of a morecomplete proximal anterior nerve tarsal compromise syndrome beenagnosed identified, as a major then contributing consideration factor is also to deepgiven peroneal to fasciotomy. neural- orshould more be proximalruled out pathology.with examination26 Howe ofve ther, patients lower spine, may sciatic have gia, then ankle ligament reconstruction may need to be symptomsnerve, common consistent peroneal with nerve. an anterior Weakness TTS and/orwith both atrophy motor of andthe Rconsidered.esults Finally, when anterior compartment syndrome has sensoryEDB muscle nerve is compression suggestive of despite a complete lack of anterior EDB atrophy. tarsal syndrome This sit- been identified, then consideration is also given to fasciotomy. 26 uationor more is secondary proximal pathology.to an accessoryHo EDBweve r,innervation patients may from have the Based on anecdotal experience, nonoperative management is SPN,symptoms noted consistent in approximately with an anterior 22% TTS of patients.with both15,48,69 motorWhen and successfulResults when the external sources of compression or ankle in- sensorysymptoms nerve are compression reported to occurdespite in lack the ofdynamic EDB atrophy. state, the This evalu- sit- stability contributing to symptoms are eliminated. Infrequently, uationation should is secondary include to dorsiflexion an accessory and EDB plantarflexion innervation of thefrom ankle the cortisoneBased on injection anecdotal is effective experience, in treatment nonoperative of deep management peroneal neu- is SPN, noted in approximately 22% of patients.15,48,69 When successful when the external sources of compression or ankle in- symptoms are reported to occur in the dynamic state, the evalu- stability contributing to symptoms are eliminated. Infrequently, ation should include dorsiflexion and plantarflexion of the ankle cortisone injection is effective in treatment of deep peroneal neu-

45 46 Surgical ManagementSurgical Mofanagement Entrapment Neuropathies of Entrapment in the Foot,Neuropathies Including Indications in the F ootand Outcomes AAEM Course AAEM Course Painful Foot and Ankle 47 ralgia.26 Nonoperative management is generally inadequate Diagnostic Studies direct sural nerve injury, surgery adjacent to the sural nerve may Management when symptoms are secondary to soft-tissue, osteophyte, or gan- result in scar entrapment, leading to adhesive neuralgia.108 glion impingement.26 Rarely, plain radiographs may demonstrate a bony abnormality Nonoperative responsible for the compression, but typically Evaluation The experience of Dellon26 with 20 DPN entrapments managed physical examination will prompt radiographic evaluation. Soft- Nonoperative management of sural neuralgia requires identifica- with surgical decompression suggests an 80% satisfactory tissue masses may be assessed with MRI or ultrasound. The most History tion of the etiology of nerve compromise. As for any peripheral outcome. Poor results are typically related to internal nerve useful tool is the anesthetic block at the site of nerve compro- neuralgia, any other source of nerve compromise, such as sys- damage or neuropathies contributing to nerve compromise, in mise, usually in the subsartorial canal. Some clinicians have Most patients with sural nerve disorders recall a history of ankle temic illness responsible for neuralgia or more proximal sites of which case simple neurolysis usually proved ineffective.26 demonstrated that somatosensory evoked potentials may aid in injuries, typically acute or recurrent ankle sprains. Patients with nerve compression, needs to be addressed. Isolated sural neural- diagnosis of saphenous nerve entrapment.32,125 persistent pain after ankle sprains may note radiating symptoms gia may respond to NSAIDS, TCAs, antiepileptic medications, or paresthesias associated with instability. Although the pain or vitamin B6. If nerve compromise is secondary to traction from SAPHENOUS NERVE ENTRAPMENT Management pattern may be poorly localized, occasionally a focus of pain chronic ankle instability, then bracing, orthotics, or shoe modi- allows for identification of a specific area of nerve compromise fications may prove effective, as for SPN neuralgia. Caution with Overview/Etiology/Anatomy Nonoperative management may involve activity modification if along the course of the sural nerve.109 Previous surgery on the bracing is advised because external compression may aggravate symptoms have a dynamic component. Cortisone added to the lateral heel and ankle (i.e., for a calcaneus fracture, lateral ankle sural nerve symptoms. Again, symptoms failing management of Saphenous nerve entrapment or neuralgia is not common. diagnostic nerve block noted previously may prove therapeutic. reconstruction, etc.), should be documented. the sural nerve may respond to treatment directed at the SPN, Typically, entrapment of this nerve occurs about the knee, but Treating saphenous nerve entrapment with therapeutic blocks given the cross-innervation. because its terminal distribution is at the medial ankle and foot, has resulted in satisfactory relief of symptoms in 38-80% of pa- Physical Examination patients may present with medial distal lower extremity pain sec- tients.83,101 Surgical management requires release of the anterior Operative ondary to compromise of this nerve. The saphenous nerve aspect of Hunter’s canal and dissection of the saphenous/sartor- An understanding of sural nerve anatomy is essential in identi- courses with the superficial femoral artery after originating from ial nerve fibers from the surrounding fascial.67,125 fying areas of nerve entrapment from the popliteal fossa to the When a specific site of nerve compression, i.e., scar entrapment the . It penetrates the subsartorial fascia approxi- lateral foot. The overlap of the SPN and tibial peripheral nerve or local mass effect, identified on physical examination fails to mately 10 cm proximal to the medial femoral condyle and then fibers comprising the sural nerve may render the distal sensory respond to nonoperative management, then neurolysis may be divides into the infrapatellar and sartorial or distal saphenous SURAL NERVE ENTRAPMENT examination unremarkable, despite symptoms suggesting en- effective in relieving symptoms.45,93 In rare situations, neurolysis branches. The sartorial component descends along the medial trapment. A Tinel’s percussion test may be useful in localizing may involve decompression of SPN fibers as well. Should symp- tibial border with the greater saphenous vein. Approximately 15 Overview/Etiology/Anatomy foci of nerve compromise; often such findings are associated toms be related to ankle instability, then surgical stabilization cm proximal to the medial malleolus, the sartorial or distal with lateral heel/ankle surgical scars. may eliminate the dynamic etiology of sural neuralgia.110 saphenous nerve separates into two branches: one that supplies The medial sural nerve and lateral sural nerve (peroneal com- Neuroma of the nerve may warrant higher transection and burial sensation to the medial aspect of the ankle and one that inner- municating branch) combine to form the sural nerve in the In the static situation, symptoms may not be observed when into muscle, fat, or bone. vates the medial foot. Although entrapment or compression may distal third of the leg on the lateral aspect of the ankle.16,20,92 ankle instability is responsible for sural nerve entrapment pain. occur anywhere along the nerve’s course, the most likely site of Sural nerve innervation combines fibers from both the tibial and Examination should include inversion testing of the hindfoot Results compromise is at the subsartorial fascia, just proximal to the SPNs. Just proximal to the ankle, two branches of the sural nerve and ankle to identify dynamic etiologies of sural neuralgia. As for medial femoral condyle. become apparent: the lateral branch, which occasionally anasto- other peripheral nerve compromise, consideration must be given No large series reporting the results of management of sural neu- moses with the SPN, and the posterior branch, which innervates to the double-crush phenomenon126 with evaluation of the ralgia is currently available. Anecdotal experience and case Evaluation the lateral aspect of the heel.16 The posterior division continues entire leg and lumbar spine. reports suggest that occasionally nonoperative management is ef- inferior to the peroneal tendons to supply sensation to the lateral fective. Surgical decompression of mass effects (such as scar en- History foot over the proximal fifth metatarsal.16,70 This network of Diagnostic Studies trapment, ganglions, and avulsion fractures) typically results in branches is responsible for sensation on the lateral foot, heel, and satisfactory symptomatic relief.45,93,108 It has been our experience Because the nerve compromise may be proximal, it is important ankle.106 Plain radiographs should be obtained to rule out bony abnor- that sural neuralgia due to ankle instability is managed effectively to identify any history of knee injury, knee or bypass surgery, or mality that may contribute to nerve compression, and MRI may with lateral ankle stabilization, without directly addressing the pain. Direct trauma anywhere along the course of the nerve may Sural nerve entrapment may occur anywhere along its course, be helpful when a soft-tissue mass effect is suspected. sural nerve. be responsible for entrapment within scar tissue. but most commonly it is a result of ankle or lateral foot in- Electrodiagnostic studies can occasionally confirm a clinical sus- juries.110 Recurrent ankle sprains,93,110 fractures of the calcaneal picion of limited sural nerve conduction, but these tests are typ- Physical Examination base of the fifth metatarsal,45,93 peroneal and Achilles’ tendon in- ically most useful in diagnosing more proximal sites of nerve SUMMARY flammation, edema, and ganglion formation have also been compromise. Diagnostic nerve blocks are of some use in defin- Although the patient may complain of medial ankle and foot identified as causes for sural nerve compression or injury.93,109 ing sural nerve entrapment symptoms. A nerve block more prox- Nerve dysfunction of the foot and ankle may involve the tibial, pain, point tenderness is typically located over the subsartorial imal to the affected area that relieves symptoms lends support to saphenous, sural, and superficial and DPNs. The nerves may be canal proximal to the medial femoral condyle. Occasionally, hy- Surgery about the lateral heel and foot may result in iatrogenic clinical suspicions of peripheral sural nerve entrapment. An damaged chronically by repetitive stretching or repetitive contu- perextension of the knee will produce distal symptoms. In iso- sural nerve pathology.62,63 The network of sural nerve branches anesthetic nerve block failing to relieve symptoms suggests that sion. Acutely, the nerve can be stretched, contused, or transected. lated saphenous nerve compromise, no motor deficits will be often warrants traction or transection of the sural nerve in the symptoms either are derived from SPN crossover fibers or may Any of these mechanisms can result in nerve entrapment with present. The entire course of the nerve should be palpated to surgical management of calcaneus fractures, ligamentous insta- be secondary to a more proximal nerve compromise. In such sit- pain and dysfunction. Evaluating these conditions requires identify any other sites of possible nerve compromise. bility, tendon pathology, or hindfoot arthritis. Even without uations, it is prudent to perform a second selective nerve block knowledge of neural anatomy, coupled with a detailed history of the fibers contributed by the SPN. and physical examination. Supportive tests include radiographic

46 AAEM Course FOOT ANDPainful ANKLE Foot NERVE and Ankle DISORDERS 47 direct sural nerve injury, surgery adjacent to the sural nerve may Management result in scar entrapment, leading to adhesive neuralgia.108 Nonoperative Evaluation Nonoperative management of sural neuralgia requires identifica- History tion of the etiology of nerve compromise. As for any peripheral neuralgia, any other source of nerve compromise, such as sys- Most patients with sural nerve disorders recall a history of ankle temic illness responsible for neuralgia or more proximal sites of injuries, typically acute or recurrent ankle sprains. Patients with nerve compression, needs to be addressed. Isolated sural neural- persistent pain after ankle sprains may note radiating symptoms gia may respond to NSAIDS, TCAs, antiepileptic medications, or paresthesias associated with instability. Although the pain or vitamin B6. If nerve compromise is secondary to traction from pattern may be poorly localized, occasionally a focus of pain chronic ankle instability, then bracing, orthotics, or shoe modi- allows for identification of a specific area of nerve compromise fications may prove effective, as for SPN neuralgia. Caution with along the course of the sural nerve.109 Previous surgery on the bracing is advised because external compression may aggravate lateral heel and ankle (i.e., for a calcaneus fracture, lateral ankle sural nerve symptoms. Again, symptoms failing management of reconstruction, etc.), should be documented. the sural nerve may respond to treatment directed at the SPN, given the cross-innervation. Physical Examination Operative An understanding of sural nerve anatomy is essential in identi- fying areas of nerve entrapment from the popliteal fossa to the When a specific site of nerve compression, i.e., scar entrapment lateral foot. The overlap of the SPN and tibial peripheral nerve or local mass effect, identified on physical examination fails to fibers comprising the sural nerve may render the distal sensory respond to nonoperative management, then neurolysis may be examination unremarkable, despite symptoms suggesting en- effective in relieving symptoms.45,93 In rare situations, neurolysis trapment. A Tinel’s percussion test may be useful in localizing may involve decompression of SPN fibers as well. Should symp- foci of nerve compromise; often such findings are associated toms be related to ankle instability, then surgical stabilization with lateral heel/ankle surgical scars. may eliminate the dynamic etiology of sural neuralgia.110 Neuroma of the nerve may warrant higher transection and burial In the static situation, symptoms may not be observed when into muscle, fat, or bone. ankle instability is responsible for sural nerve entrapment pain. Examination should include inversion testing of the hindfoot Results and ankle to identify dynamic etiologies of sural neuralgia. As for other peripheral nerve compromise, consideration must be given No large series reporting the results of management of sural neu- to the double-crush phenomenon126 with evaluation of the ralgia is currently available. Anecdotal experience and case entire leg and lumbar spine. reports suggest that occasionally nonoperative management is ef- fective. Surgical decompression of mass effects (such as scar en- Diagnostic Studies trapment, ganglions, and avulsion fractures) typically results in satisfactory symptomatic relief.45,93,108 It has been our experience Plain radiographs should be obtained to rule out bony abnor- that sural neuralgia due to ankle instability is managed effectively mality that may contribute to nerve compression, and MRI may with lateral ankle stabilization, without directly addressing the be helpful when a soft-tissue mass effect is suspected. sural nerve. Electrodiagnostic studies can occasionally confirm a clinical sus- picion of limited sural nerve conduction, but these tests are typ- ically most useful in diagnosing more proximal sites of nerve SUMMARY compromise. Diagnostic nerve blocks are of some use in defin- ing sural nerve entrapment symptoms. A nerve block more prox- Nerve dysfunction of the foot and ankle may involve the tibial, imal to the affected area that relieves symptoms lends support to saphenous, sural, and superficial and DPNs. The nerves may be clinical suspicions of peripheral sural nerve entrapment. An damaged chronically by repetitive stretching or repetitive contu- anesthetic nerve block failing to relieve symptoms suggests that sion. Acutely, the nerve can be stretched, contused, or transected. symptoms either are derived from SPN crossover fibers or may Any of these mechanisms can result in nerve entrapment with be secondary to a more proximal nerve compromise. In such sit- pain and dysfunction. Evaluating these conditions requires uations, it is prudent to perform a second selective nerve block knowledge of neural anatomy, coupled with a detailed history of the fibers contributed by the SPN. and physical examination. Supportive tests include radiographic

47 48 Surgical ManagementSurgical Mofanagement Entrapment Neuropathies of Entrapment in the Foot,Neuropathies Including Indications in the F ootand Outcomes AAEM Course and EDX studies. Selective nerve injections are most useful in 20. Coert JH, Dellon AL. Clinical implications of the surgical anatomy isolating the site of the nerve dysfunction. Whenever possible, of the sural nerve. Plast Reconstr Surg 1994;94:850-855. treatment is directed toward decreasing symptoms with braces, 21. Cohen SJ. Another consideration for the diagnosis of heel pain -- neuroma of the medial calcaneal nerve. J Foot Surg 1974;13:128- local cortisone injections, or various medications (NSAIDS, 130. TCAs, and antiepileptics). When these measures fail, surgical 22. Cozen L. Bursitis of the heel. Am J Orthop 1961;3:372-372. release of the nerve, addressing the underlying pathology, will 23. Cracchiolo A, Cimino WR, Lian G. 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Nerve entrapment in painful heel syndrome. Foot Ankle Int talgia paresthetica among recruits. Foot Ankle 1989;9:312-313. 2002;23:208-211.

50 50 Surgical Management of Entrapment Neuropathies in the Foot, Including Indications and Outcomes AAEM Course

94. Radin EL. Tarsal tunnel syndrome. Clin Orthop 1983;181:167-170. 118. Styf J. Diagnosis of exercise-induced pain in the anterior aspect of the 95. Rask MR. Medial plantar neurapraxia (jogger’s foot): report of 3 lower leg. Am J Sports Med 1988;16:165-169. cases. Clin Orthop 1978;134:193-195. 119. Styf J. Entrapment of the superficial peroneal nerve. Diagnosis and 96. Rasmussen MR, Kitaoka HB, Patzer GL. Nonoperative treatment of results of decompression. J Bone Joint Surg Br 1989;71:131-135. plantar interdigital neuroma with a single corticosteroid injection. 120. Styf JR, Korner LM. Chronic anterior-compartment syndrome of the Clin Orthop 1996;326:188-193. leg. Results of treatment by fasciotomy. J Bone Joint Surg Am 97. Redd RA, Peters VJ, Emery SF, Branch HM, Rifkin MD. Morton 1986;68:1338-1347. neuroma: sonographic evaluation. Radiology 1989;171:415-417. 121. Taguchi Y, Nosaka K, Yasuda K, Teramoto K, Mano M, Yamamoto 98. Resch S, Stenstrom A, Jonsson A, Jonsson K. The diagnostic efficacy S. The tarsal tunnel syndrome. Report of two cases of unusual cause. of magnetic resonance imaging and ultrasonography in Morton’s Clin Orthop 1987;217:247-252. neuroma: a radiological-surgical correlation. Foot Ankle Int 122. Takakura Y, Kitada C, Sugimoto K, Tanaka Y, Tamai S. Tarsal tunnel 1994;15:88-92. syndrome. Causes and results of operative treatment. J Bone Joint Foot and Ankle Nerve Disorders 99. Richardson EG, Brotzman SB, Graves SC. The plantar incision for Surg Br 1991;73:125-128. procedures involving the forefoot. An evaluation of one hundred and 123. Tanz SS. Heel pain. Clin Orthop 1963;28:169-177. CME Questions fifty incisions in one hundred and fifteen patients. J Bone Joint Surg 124. Terk MR, Kwong PK, Suthar M, Horvath BC, Colletti PM. Morton Am 1993;75:726-731. neuroma: evaluation with MR imaging performed with contrast en- 100. Roegholt MN. Een nervus calcaneus inferior als overbrenger van de hancement and fat suppression. Radiology 1993;189:239-241. pijn bij calcaneodynie of calcanenesspoor en de daaruit volgende ther- 125. Tranier S, Durey A, Chevallier B, Liot F. Value of somatosensory apie. Ned Tijdschr v Geneeskd 1940;84:1898-1902. evoked potentials in saphenous entrapment neuropathy. J Neurol 1. Entrapment sites for tibial nerve branches in the foot include 8. Which of the following is NOT true about medial calcaneal 101. Romanoff ME, Cory PC Jr, Kalenak A, Keyser GC, Marshall WK. Neurosurg Psychiatry 1992;55:461-465. all of the following EXCEPT: nerve entrapment? Saphenous nerve entrapment at the adductor canal. Am J Sports Med 126. Upton AR, McComas AJ. The double crush in nerve entrapment A. The inferior extensor retinaculum. A. It can occur where the nerve passes through the fascia 1989;17:478-481. syndromes. Lancet 1973;2:359-362. B. The abductor canals. overlying the medial calcaneus. 102. Rondhuis JJ, Huson A. The first branch of the lateral plantar nerve 127. Wapner KL, Sharkey PF. The use of night splints for treatment of re- C. The interfascicular septum. B. It can cause a “lamp-cord sign.” and heel pain. Acta Morphol Neerl Scand 1986;24:269-279. calcitrant plantar fasciitis. Foot Ankle 1991;12:135-137. D. The calcaneal chambers. C. It can result in fibrillation potentials and positive sharp 103. Rydevik B, McLean WG, Sjostrand J, Lundborg G. Blockage of 128. Weinfeld SB, Myerson MS. Diagnosis and treatment of Morton’s waves in the abductor hallucis. axonal transport induced by acute, graded compression of the rabbit neuroma. JAAOS 1996;4:328-335. 2. Symptoms of tarsal tunnel syndrome (TTS) tend to improve D. It can be caused by shoe-wear. vagus nerve. J Neurol Neurosurg Psychiatry 1980;43:690-698. 129. Zeiss J, Fenton P, Ebraheim N, Coombs RJ. Magnetic resonance at night and worsen during the day. 104. Sammarco GJ, Chalk DE, Feibel JH. Tarsal tunnel syndrome and ad- imaging for ineffectual tarsal tunnel surgical treatment. Clin Orthop A. True 9. Regarding motor NCSs of the tibial nerve branches in the ditional nerve lesions in the same limb. Foot Ankle 1993;14:71-77. 1991;264:264-266. B. False foot: 105. Sammarco GJ, Stephens MM. Tarsal tunnel syndrome caused by the A. The stimulation site is the same for all 3 motor flexor digitorum accessorius longus. A case report. J Bone Joint Surg CURRENT SUGGESTED READING Am 1990;72:453-454. 3. Which of the following is NOT a needle electrymyography branches. 106. Sarrafian SK. Anatomy of the foot and ankle. Descriptive, topo- (EMG) match? B. E1 placement for the LPN is the midpoint of the 5th 1. Bennett GL, Graham CE, Mauldin DM. Morton's interdigital graphic, functional. Philadelphia: JB Lippincott Co; 1983. A. Medial plantar nerve => abductor hallucis. metatarsal. neuroma: a comprehensive treatment protocol. Foot Ankle Int 107. Schon LC. Plantar fascia and Baxter’s nerve release. In: Myerson M, B. Lateral plantar nerve => 4th dorsal interosseus pedis. C. E1 placement for the inferior calcaneal nerve 1995;16:760-763. editor. Current therapy in foot and ankle surgery. St. Louis: Mosby- C. Deep peroneal nerve => extensor digitorum brevis. (“Baxter’s nerve) is midway between the lateral 2. Coughlin MJ, Pinsonneault T. Operative treatment of interdigital Year Book Inc; 1993. p 177-182. neuroma. A long-term follow-up study. J Bone Joint Surg Am D. Inferior calcaneal nerve => flexor digiti minimi brevis. malleolus and the sole. 108. Schon LC. Nerve entrapment, neuropathy, and nerve dysfunction in 2001;83:1321-1328. D. E1 placement for the MPN is the midpoint of the 1st athletes. Orthop Clin North Am 1994;25:47-59. 3. Coughlin MJ, Schenck RC Jr, Shurnas PS, Bloome DM, Shurnas PJ. 4. For the diagnosis of TTS, medial palmar nerve (MPN) metatarsal. 109. Schon LC, Baxter DE. Neuropathies of the foot and ankle in athletes. Concurrent interdigital neuroma and MTP joint instability: long- and lateral palmar nerve (LPN) sensory or mixed nerve Clin Sports Med 1990;9:489-509. term results of treatment. Foot Ankle Int 2002;23:1018-1025. conduction studies (NCSs) are more sensitive than MPN and 10. Motor, sensory, and mixed nerve conduction studies (NCSs) 110. Schon LC, Baxter DE. Heel pain syndrome and entrapment neu- 4. Frey C, Kerr R. Magnetic resonance imaging and the evaluation of ropathies about the foot and ankle. In: Gould JS, editor. Operative LPN motor NCSs. along with needle EMG can assist in confirming the diagnosis tarsal tunnel syndrome. Foot Ankle 1993;14:159-164. foot surgery. Philadelphia: WB Saunders Co; 1994. p 192-208. A. True. of TTS in up to 90% of cases. 5. Gondring WH, Shields B, Wenger S. An outcomes analysis of surgi- 111. Schon LC, Easley ME. Chronic pain. In: Myerson MS, editor. Foot B. False. A. True. cal treatment of tarsal tunnel syndrome. Foot Ankle Int 2003;24:545- and ankle disorders. Philadelphia: WB Saunders Co; 2000. p 851- B. False. 550. 881. 5. Entrapment neuropathies involving individual tibial nerve 6. Hort KR, DeOrio JK. Adjacent interdigital nerve irritation: single in- 112. Schon LC, Glennon TP, Baxter DE. Heel pain syndrome: electrodi- branches in the foot are more common than “classic” TTS. 11. Which of the following is not innvervated by Baxter’s cision surgical treatment. Foot Ankle Int 2002;23:1026-1030. agnostic support for nerve entrapment. Foot Ankle 1993;14:129- 7. Kinoshita M, Okuda R, Morikawa J, Abe M. Tarsal tunnel syndrome A. True. nerve? 135. associated with an accessory muscle. Foot Ankle Int 2003;24:132- B. False. A. Abductor digiti quinti pedis. 113. Seiler JG. Double crush syndrome: experiemental model in the rat. 136. B. Medial calcaneal tuberosity. Forum 1983;34:597-597. 8. Labib SA, Gould JS, Rodriguez-del-Rio FA, Lyman S. Heel pain triad 6. The most common cause of TTS is: C. Abductor halluces. 114. Shapiro PP, Shapiro SL. Sonographic evaluation of interdigital neu- (HPT): the combination of plantar fasciitis, posterior tibial tendon A. Space-occupying lesions. D. Quadratus plantae. romas. Foot Ankle Int 1995;16:604-606. dysfunction and tarsal tunnel syndrome. Foot Ankle Int 115. Skalley TC, Schon LC, Hinton RY, Myerson MS. Clinical results fol- B. Systemic causes (such as diabetes mellitus). 2002;23:212-220. lowing revision tibial nerve release. Foot Ankle Int 1994;15:360-367. C. Trauma and post-traumatic changes. 12. What would be the predominant symptom reported by a 9. Lau JT, Daniels TR. Effects of tarsal tunnel release and stabilization 116. Stack RE, Bianco AJ, Jr., MacCarty CS. Compression of the D. Idiopathic. patient with Baxter’s neuropathy? procedures on tibial nerve tension in a surgically created pes planus common peroneal nerve by ganglion cysts: report of nine cases. J A. Paresthesia in the heel. foot. Foot Ankle Int 1998;19:770-777. Bone Joint Surg Am 1965;47:773-778. 7. Regarding the clinical presentation of TTS, the differential B. Pain in the medial/plantar aspect of the heel. 10. Oztuna V, Ozge A, Eskandari MM, Colak M, Golpinar A, Kuyurtar 117. Stein M, Shlamkovitch N, Finestone A, Milgrom C. Marcher’s digi- diagnosis includes all of the following EXCEPT: C. Weakness of the little toe abductor. F. Nerve entrapment in painful heel syndrome. Foot Ankle Int talgia paresthetica among recruits. Foot Ankle 1989;9:312-313. 2002;23:208-211. A. Jogger’s foot. D. Diminished Achilles reflex on the affected side. B. Plantar fasciitis. C. L5/S1 radiculopathy. D. Peripheral arterial disease.

51 CME QUESTIONS 13. Which of the following is NOT considered to be a terminal 17. Which one of the following is the most common problem in branch of the tibial nerve? the hind foot? A. Baxter’s nerve. A. Heel pad atrophy. B. The medial plantar nerve. B. Retrocalcaneal bursitis. C. The medial calcaneal nerve. C. Achilles tendonitis. D. The saphenous nerve. D. Plantar fasciitis. E. Calcaneal stress fracture. 14. All of the following are names given to the nerve which innervates the abductor digiti quinti pedis (ADQP) muscle 18. Which of the following statements about the posterior tibial EXCEPT: tendon is true? A. The lateral calcaneal nerve. A. It everts the hind foot during toe-off. B. Baxter’s nerve. B. Problems with it lead to the development of pes cavus. C. 1st branch of the lateral plantar nerve. C. It serves to balance the pull of the peroneal tendons. D. The inferior calcaneal nerve. D. Inflammation of it results in medial foot pain.

15. Based on the information presented in this article, the most 19. Haglund’s syndrome involves all of the following, likely electrophysiologic abnormality in a patient with EXCEPT: Baxter’s neuropathy would be: A. Insertional tendonitis. A. Reduced Baxter’s nerve compound muscle action B. Retrocalcaneal bursitis. potential amplitude. C. Enlarged bursal prominence. B. Prolonged distal onset latency of Baxter’s nerve. D. Isolated pump bump. C. Sustained fibrillation potentials and/or positive sharp E. Adentitial bursitis. waves in the ADQP. D. Sustained fibrillation potentials and/or positive sharp 20. Which one of the following is true about hallux rigidus? waves in the flexor digitorum brevis. A. It is arthritis of the first metatarsophalangeal joint. B. It usually does not cause pain. 16. Which ligament is involved most commonly in a foot C. Is associated with diabetes mellitus. inversion injury (ankle sprain)? D. Is caused by the contracture of the extensor halluces A. Calcaneal fibular. longus tendon B. Posterior talofibular. E. It develops as a result of pes planus (flat foot). C. Anterior talofibular. D. Tibiocalcaneal. 21. The most common location of an interdigital neuroma is E. None of the above. the: A. Medial great toe. B. 1st webspace. C. 3rd webspace. D. Lateral little toe.

52 Capturing Motion with Ultrasound: Blood, Muscle, Needle, and Nerve

Francis O. Walker, MD Einer P. Wilder-Smith, MD, DTM&H Michael S. Cartwright, MD Andrea J. Boon, MD, MBChB John W. Norbury, MD

AANEM 58th Annual Meeting San Francisco, California

Copyright © September 2011 American Association of Neuromuscular & Electrodiagnostic Medicine 2621 Superior Drive NW Rochester, MN 55901

Printed by Johnson’s Printing Company, Inc. 1 Please be aware that some of the medical devices or pharmaceuticals discussed in this handout may not be cleared by the FDA or cleared by the FDA for the specific use described by the authors and are “off-label” (i.e., a use not described on the product’s label). “Off-label” devices or pharmaceuticals may be used if, in the judgment of the treating physician, such use is medically indicated to treat a patient’s condition. Information regarding the FDA clearance status of a particular device or pharmaceutical may be obtained by reading the product’s package labeling, by contacting a sales representative or legal counsel of the manufacturer of the device or pharmaceutical, or by contacting the FDA at 1-800-638-2041.

2 Capturing Motion With Ultrasound: Blood, Muscle, Needle, and Nerve

Table of Contents

Course Objectives & Course Committee 4

Faculty 5

Basic Principles of Imaging Movement With Ultrasound 7 Francis O. Walker, MD

Ultrasound and Blood Flow Imaging in the Diagnosis of Entrapment Neuropathy 15 Einar P. Wilder-Smith, MD, DTM&H

Dynamic Ultrasound in the Assessment of Focal Neuropathies 19 Michael S. Cartwright, MD

Ultrasound Imaging of the Diaphragm and as an Adjunct to Electrodiagnosis 23 Andrea J. Boon, MD, MBChB

Intervential Neuromuscular Ultrasound 29 John W. Norbury, MD

CME Quiz Questions 35

No one involved in the planning of this CME activity had any relevant financial relationships to disclose. Authors/faculty have nothing to disclose.

Course Chair: Francis O. Walker, MD

The ideas and opinions expressed in this publication are solely those of the specific authors and do not necessarily represent those of the AANEM.

3 Objectives

Objectives - Participants will acquire skills to (1) list five indications for performing NM US in children, (2) describe how US can be used to guide interventional therapy, (3) discuss the use of US in tracking changes in nerve and muscle disease over time, and (4) define four basic concepts in US physics: attenuation, anisotropy, time gain compensation, and brightness mode imaging. Target Audience: • Neurologists, physical medicine and rehabilitation and other physicians* interested in neuromuscular and electrodiagnostic medicine • Health care professionals involved in the management of patients with neuromuscular diseases • Researchers who are actively involved in the neuromuscular and/or electrodiagnostic research Physicians who are eligible to attend the AANEM meeting are MDs, DOs, and overseas equivalents. Healthcare Professionals and Researchers who are not AANEM members must receive a letter of support from a Fellow AANEM member to attend the meeting. Accreditation Statement - The AANEM is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education (CME) for physicians. CME Credit - The AANEM designates this live activity for a maximum of 3.25 AMA PRA Category 1 CreditsTM. If purchased, the AANEM designates this enduring material for a maximum of 4.75 AMA PRA Category 1 CreditsTM. This educational event is approved as an Accredited Group Learning Activity under Section 1 of the Framework of Continuing Professional Development (CPD) options for the Maintenance of Certification Program of the Royal College of Physicians and Surgeons of Canada. Physicians should claim only the credit commensurate with the extent of their participation in the activity. CME for this course is available 09/2011 - 09/2014. CEUs Credit - The AANEM has designated this live activity for a maximum of 3.25 AANEM CEUs. If purchased, the AANEM designates this enduring material for a maximum of 4.75 CEUs.

2010-2011 Course Committee

Shawn J. Bird, MD, Chair Taylor B. Harrison, MD A. Arturo Leis, MD Philadelphia, PA Atlanta, GA Jackson, MS

Gary L. Branch, DO Laurence J. Kinsella, MD Marcy C. Schlinger, DO Owosso, MI Saint Louis, MO Okemos, MI

Lawrence W. Frank, MD Shashi B. Kumar, MD Benjamin S. Warfel, MD Elmhurst, IL Tacoma, WA Lancaster, PA

2010-2011 AANEM President

Timothy R. Dillingham, MD, MS Milwaukee, Wisconsin

4 Capturing Motion With Ultrasound: Blood, Muscle, Needle, and Nerve Faculty

Andrea J. Boon, MD, MBChB in the MDA Clinic, Amyotrophic Lateral Sclerosis (ALS) Clinic, Assistant Professor and Electromyography Laboratory. His research interests include Departments of Physical Medicine and Rehabilitation neuromuscular ultrasound and other imaging modalities for and Neurology neuromuscular disease, and therapeutic trials in ALS. He is co- Mayo Clinic College of Medicine editor of Neuromuscular Ultrasound (Elsevier 2011), the first Rochester, Minnesota textbook dedicated to the field of neuromuscular US.

Dr. Boon graduated from medical school in New Zealand before John W. Norbury, MD completing her residency in physical medicine and rehabilitation Clinical Assistant Professor of Physical Medicine which was followed by a fellowship in clinical neurophysiology and Rehabilitation at the Mayo Clinic, Rochester, Minnesota. She has been on Director of the Musculoskeletal Ultrasound Laboratory staff at the Mayo Clinic College of Medicine since 2000, with The Brody School of Medicine a joint appointment as assistant professor in the departments of East Carolina University physical medicine and rehabilitation and neurology. Dr. Boon Greenville, North Carolina has introduced diagnostic ultrasound (US) into the clinical and academic practice of the Mayo electromyography laboratory, Dr. Norbury received his bachelor of science degree in molecular where more than 12,000 patients undergo electrodiagnostic testing biophysics and biochemistry from Yale University and his annually. Her current research focus is in this area, in addition medical degree from Case Western Reserve University with to her musculoskeletal practice where she has been investigating a minor in geriatrics. He completed an internship in internal the role of botulinum toxin in painful musculoskeletal disorders. medicine at MetroHealth Medical Center in Cleveland, Ohio, Dr. Boon is a member of the Continuing Medical Education and a residency in rehabilitation medicine at Thomas Jefferson committee of the American Academy of Physical Medicine and University in Philadelphia, Pennsylvania, where he served Rehabilitation and the Professional Practice committee of the as chief resident in 2010. He has received numerous awards American Association of Neuromuscular & Electrodiagnostic for medical student teaching, medical student curriculum Medicine (AANEM), as well as serving as the AANEM Current development, and research. He has published papers, presented Procedural Terminology (CPT®) Advisor and the AANEM abstracts, and lectured extensively on geriatric rehabilitation and Alternate Relative Value Update Committee (RUC) Advisor to musculoskeletal ultrasound (US). His research interests include the American Medical Association. US, geriatric rehabilitation, geriatric musculoskeletal medicine, electrodiagnosis, and trauma rehabilitation. Michael S. Cartwright, MD Assistant Professor of Neurology Francis O. Walker, MD Wake Forest School of Medicine Professor of Neurology Winston-Salem, North Carolina Director of the EMG Laboratory Wake Forest University Michael Cartwright completed medical school at Wake Forest Winston-Salem, North Carolina School of Medicine and a residency in neurology at Wake Forest Baptist Medical Center. He completed a 2-year fellowship in Dr. Walker is currently professor of neurology and director of the clinical research in neuromuscular disease, sponsored by the Electromyography (EMG) Laboratory at Wake Forest University. Muscular Dystrophy Association (MDA), and he is now an He is a longtime member of the American Association of assistant professor of neurology at Wake Forest School of Medicine Neuromuscular & Electrodiagnostic Medicine (AANEM) and has in Winston-Salem, North Carolina. He has clinical responsibilities served on more than eight separate committees and task forces. He

5 currently chairs the Ultrasound Task Force of the AANEM. He has presented numerous -on workshops, conducted courses, and organized symposia for AANEM. He has trained 35 EMG fellows, received the Class of 1997 Teaching Award at Wake Forest School of Medicine, and has authored or co-authored more than 100 papers in peer reviewed journals. Currently, he is on the Examination Committee of the American Board of Neuromuscular Medicine and serves on the steering committees of three major multicenter clinical trials. His interest in neuromuscular ultrasound dates back to the mid-1980s when he began exploring the technique for its use in characterizing myopathies and evaluating fasciculations.

Einar P. Wilder-Smith, MD, DTM&H Professor, Division of Neurology Director, Neurology Diagnostic Laboratory National University Singapore Singapore Senior Consultant, Spinal Injury Center University Hospital Heidelberg Heidelberg, Germany

Dr. Wilder-Smith is professor in the Division of Neurology at the National University Singapore and leads the Neurology Diagnostic Laboratory. He is a longtime member of the International Federation of Clinical Neurophysiology and past president and now vice-president of the Clinical Neurophysiology Society of Singapore. He has presented at numerous local and international conferences, workshops, and courses, particularly in the field of peripheral nerve disorders. He has authored or coauthored more than 100 papers in international peer reviewed journals and has written a book on ultrasound (US) of the peripheral nerves. One of his major research interests is on the use of US for the diagnosis of peripheral nerve diseases and a particular interest has been the study and characterisation of blood flow to the nerves.

6 Basic Principles of Imaging Movement with Ultrasound

Francis O. Walker, MD Professor of Neurology Director of the EMG Laboratory Wake Forest School of Medicine Winston-Salem, North Carolina

Ultrasound Physics In The Detection Of pulse of sound followed by a long period where it records the Blood Flow And Movement Of Tissue returning echoes. In A-mode, or amplitude mode, each transducer unit displays a typical oscilloscope type trace of the intensity Ultrasound (US) has a variety of attractive qualities as a of the sound echo received on the vertical axis, and latency or neuromuscular imaging instrument including portability, ease of time on the horizontal axis. However, multiple A-mode displays, use, lack of discomfort for patients, excellent edge resolution, and although useful for comparisons of relative amplitudes, do not low cost. Of particular interest, however, is its ability to image in provide a useful graphic of anatomy. In gray scale US, known real time, a property which makes it an ideal tool for imaging the also as B-mode (brightness mode), the display is rotated 90 mechanics of movement, muscle contraction, pathologic muscle degrees, so that time is on the vertical axis, with the earliest activity (including fasciculations and fibrillations), kinesiology, returning echoes represented at the top of the screen and later needle movement in tissue, and blood flow.1-3 An understanding returning echoes at correspondingly greater depths. Because the of the physical principals of US involved in real-time imaging speed of sound is relatively constant in tissue, depth on the screen will help to optimize the use of these instruments in the care of actually correlates with depth in tissue. The amplitude of these patients. echoes is coded, not as a deviation on the horizontal axis (which would create a confusing tangle of intersecting lines from each Because this discussion will focus on imaging of movement, transducer), rather, as varying degrees of brightness. This way, the basic principles of static US imaging will only be covered each transducer can produce information uncontaminated by input briefly. A more thorough discussion of these fundamentals can be from its neighbors, and each has the independent task of mapping found in other sources.2,4,5 Key elements reviewed will include: a tiny strip of tissue directly below it when it is applied to the (1) frame rate, (2) spatial and temporal resolution, (3) M-mode skin. By seamlessly stitching together the input from adjacent imaging, (4) color Doppler imaging, (5) power Doppler imaging, transducer elements in the array, anatomic features in the plane of and (6) contrast enhanced US. the linear transducer, detailed in terms of both depth and width, can be displayed as a two dimensional image. This is updated Basic Imaging Principles continually to provide information on the third dimension of time. The process is similar to creating a television image from multiple The action end of the US instrument is the probe (or transducer) lines of streaming input.1,2,5,6 which, in neuromuscular US, is a bit of a misnomer since it typically refers to a linear array of multiple tiny transducers. M-Mode Imaging Each individual transducer element in this array has the task of mapping a small core of tissue directly in the path of the sound M-mode images provide a graphic depiction of how US works. beam it generates. It does this by insonating tissue with a brief For M-mode imaging, the input from only a single transducer 7 BASIC PRINCIPLES OF IMAGING MOVEMENT WITH ULTRASOUND in the wide array is selected, and it is displayed as it changes focal zone on US. By reducing the out of plane dimension at this over time (with recordings from right [earliest] to left [latest]). level, better spatial resolution is achieved. Every image has a least This type of display correlates well with what is seen on needle one focal zone. Multiple focal zones, created by the averaging electromyography (EMG). Note that the M-mode trace looks like of successive sound pulses that modulate the focal zone, reduce a series of brighter and darker bands going across the screen, temporal resolution. Again, the examiner needs to decide what in which is all that each transducer can display. A coincident real- the image needs emphasis: spatial resolution at multiple layers or time gray scale image usually is displayed above the M-mode temporal resolution of a movement. When imaging a small nerve, image to provide anatomic orientation. A disturbance in the bands a single focal zone usually is all that is needed.2,5,6 indicates focal movement, which can be measured in terms of temporal factors (right to left) or anatomical displacement (up and Other factors can influence temporal resolution of the image down) (Figs. 1 and 2).1,2,5-7 as well. Excessive depth of penetration of sound may reduce temporal resolution, as the instrument needs to obtain data from Time Gain Compensation the latest returning echoes before the image can be refreshed and create another frame. Fortunately, in most neuromuscular imaging Of course, the actual creation of the US image requires multiple depth requirements are limited. With sector US probes, or other steps. It helps to discuss one of these, which is time gain types of probes with moving transducers (e.g., intravascular US), compensation. Echoes returning from deeper layers are much the width of the image (number of scan lines) may also affect weaker than those returning from superficial layers, because sound temporal resolution.2 energy attenuates as it travels through human tissue. As such, each instrument uses proprietary software to amplify later echoes (those Of course, when viewing movement with US, both spatial and that come from more distant structures) so that a similar structural temporal resolutions are important so no one formula can be used interface that is deep creates an echo of equivalent intensity to to specify imaging tactics. Even when using US to examine focal one that is superficial. Of course, some tissues attenuate sound lesions, particularly nerves where scanning along their length more than others, so there is invariably a time gain compensation is important, adjustments of spatial and temporal resolution override panel available on each instrument to either ramp up the are of value. Temporal resolution is of importance when either amplification of echoes at a given layer or set of layers if they are the patient is moving or the transducer is moving; with low deep to tissue that attenuate sound extensively (e.g., scar tissue), temporal resolution images created by moving the transducer or to ramp down the amplification of echoes if they are deep to while searching for an optimal imaging plane can be difficult to structures that attenuate sound very little (e.g., fluid filled cyst). follow.2,5,6 Those interested in this property will appreciate it best by actual hands-on manipulation of the time gain compensation levers Quantifying Tissue Movement during real-time imaging (Fig. 3).2,6 One of the problems with evaluating movement with US is Averaging determining how to measure what is observed. Some types of measurements are relatively easy. For example, muscle Another step in creating an image is averaging. The data in each contraction can be measured by the difference between the line of the display must be coordinated with its neighbor to present thickness of muscle at rest and during full contraction. Of course, a coherent picture of what is occuring in the tissue beneath the the notion of muscle thickening, which is simple at first glance, transducer. It may help to scan the same image more than once is really a bit complicated. First, muscle thickness is sensitive to and average the result before displaying it. Some high resolution probe pressure, particularly with muscle in the relaxed state. This add-ons in instruments (e.g., X resolution) involve averaging is easily demonstrated by simply applying gradually increasing multiple scans of the same tissue from slightly different angles or pressure on a relaxed muscle and observing how much its thickness transducers in the array. This image enhancing feature improves decreases; in some muscles this can be 50% or more. With a the resolution of a static image, but it should be noted, that the contracted muscle, probe pressure has far less of an effect. With averaging involved leads to a proportional loss of temporal contraction, however, parts of the muscle thicken, and other parts resolution. Instruments label functions such as averaging in narrow or become thin. After all, there is no net increase in muscle different ways, sometimes it is referred to as persistence. For those volume with contraction; in fact, if anything there is a slight loss interested in capturing tissue movement, however, it is important of volume as venous blood (and sometimes even arterial blood) to understand these functions on the instrument in use so as to disgorges from a fully contracted muscle. The biceps, a fusiform maximize the image qualities desired by the examiner.2,5,6 muscle, thickens centrally and thins peripherally with contraction. Muscles that are bipennate or multipennate have more complex The choice of the number of focal zones also influences temporal patterns of thickening and thinning with contraction resolution of the image. The focal zone on an instrument refers (Figs. 1 and 2).8-10 to narrowing the field examined perpendicular to the plane of the transducer. A static US image is a bit like a slice from a computed The duration of a muscle contraction actually is relatively easy to tomography (CT) or magnetic resonance (MR) scan where pixels measure. When this author first studied fasciculations with US in are used to represent information actually present in a three the 1980s, fasciculation duration was measured by counting frames dimensional cube of space. However, unlike CT or MR slices, on videotapes directly recorded from the real-time images (these the thickness of an US slice varies (it is variably convex) with had both time codes and a standard 30 frames/s videotape rate).11 depth of sound penetration, and it is narrowest in the area of the There are other simpler ways to measure duration. For example, 8 CAPTURING MOTION WITH ULTRASOUND: BLOOD, MUSCLE, NEEDLE, NERVE

A T

I F

A

I

Figure 1A. This is an M-mode recording of a cross-sectional image Figure 2A. This is an M-mode recording of the anterior tibialis similar to through the extensor digitorum brevis, initially at rest, punctuated by Figure 1. In the axial image of the tibialis anterior above, note the bright a brief volitional contraction in the muscle. At the top, for orientation, a bone edge of the tibia (T) is to the right, the fibular(F) in the lower left, and B-mode cross section is shown and the small vertical line on the top of the connecting interosseus membrane (I). The vertical line that bisects this this image represents the single vertical line of transducer data that is image is the line of data that is shown in the image below, swept over time. shown on the M-mode tracing below it, which is shown for 4 consecutive The arrows show the homology of the two figures by showing where the seconds including the brief voluntary twitch. Note the robust thickening vertical line crosses the aponeurosis (A) and the interosseus membrane of the muscle in its contraction phase and the time course of contraction (I). Note that the aponeurosis of the muscle constitutes the brightest band and relaxation. The arrow, in the top image, points to where the vertical in the M-mode trace. With a maximal voluntary twitch, this muscle does not line crosses the collagen rich and bright epimysium at the bottom edge of thicken as much as the extensor digitorum brevis (EDB) did in Figure 1; the the muscle, and in the lower image the arrow points to its corresponding EDB, like the biceps, is fusiform whereas the tibialis anterior is bipennate, location in the M-mode trace. and, therefore, does not have as much central thickening. The duration of the muscle contraction is approximately the same as with the EDB, but in this tracing the sweep speed is faster (2 s), showing the contraction in more detail.

200 μV 1 s

200 μV Figure 1B. This is a surface electromyography (EMG) recording of the 200 ms same contraction, shown at a slow sweep speed (note the calibration of 1 s in duration and 200 μV in amplitude). The duration of the mechanical contraction by ultrasound significantly exceeds the duration of the surface EMG recording, reflecting the difference between the real time work of muscle contraction versus the shorter duration changes in membrane Figure 2B. This is the surface electromyography recording from the twitch potential recorded by surface EMG. in the tibialis anterior recorded with surface electrodes that produced the recording shown in Figure 3. Note the sweep speed is 200 ms and the amplitude is 200 μV.

9 BASIC PRINCIPLES OF IMAGING MOVEMENT WITH ULTRASOUND

1 N T?

A

Figure 4. This is an axial M-mode tracing through the belly of the abductor hallucis muscle in an individual with benign fasciculations. Note the multiple focal perturbations in the M-mode trace (vertical arrows), each representing a fasciculation, and note that the second and fourth fasciculations have an identical footprint (curved arrows) suggesting that they are recurrent from the same motor unit. Note that the fasciculations do not incorporate the entire thickness of the muscle and thus are readily distinguished from voluntary contractions seen in Figure 1 or Figure 2. 1 N T and extension).12-14 Although the tendons clearly move distal and proximal, it is difficult to measure exactly how much movement is present. In like manner, it is difficult to measure how much the nerve moves in these directions as well. Although clearly the nerve moves less than the tendons, no set measurement can easily be obtained. subluxation can be demonstrated on still B images which show changes in location of the nerve relative to the medial epicondyle; but the actual time sequence of events, the Figure 3. These two images are virtually identical axial views of the median speed with which the nerve dislocates and the interaction of the nerve (N) in the palm, 1-2 cm distal to the distal crease in the thickest nerve with the triceps muscle, is not obvious from still images. part of the hand. In A, the time gain compensation is adjusted to enhance Pressure from the transducer itself may influence the process of the amplitude of the superficial echoes and reduce the amplitude of deep subluxation. Similarly, the lateral, diving movement of the median echoes, and as such, it is difficult to identify the tendon (T?) adjacent and nerve in the carpal tunnel with flexion of the fingers and wrist below the (N); however, the transverse carpal ligament (l) can be captured by showing extremes of movement on the still is readily identified as is the superficial palmar anatomy. In B, in which the images, but not in any other simple meaningful way.. gain is adjusted to minimize the superficial tissue and maximize the deep tissue, the tendon (T) is readily identified deep to the transverse carpal Color Doppler Imaging ligament (1) and adjacent to the nerve (N), but the palmar anatomy is not well seen. Adjusting the time gain compensation panel can thus help to Much of the early excitement about US derived from its potential clarify structures at different levels in an image. to image blood flow in the heart and major vessels, findings of critical relevance to common disabling disorders such as valvular disease, atherosclerosis, and congestive heart failure. US M-mode recordings (Fig. 4) can be used to measure duration either developed sophisticated ways to measure blood flow long before of fasciculations, supramaximal compound muscle contractions, noninvasive CT and MR angiography were routinely available. or tremor bursts. To this author’s knowledge, the duration of Although uncommonly used in this way, the same technology that fibrillations (the mechanical equivalent of the electrically recorded measures blood flow also can be adapted to measure movement of fibrillation potential) has not been calculated. Based on published other body tissues (e.g., tendons).13 videotapes of these movements, it would seem to be significantly less than the duration of fasciculations, but hard data is not yet Blood flow itself is of interest for several reasons. Perhaps most available (Fig. 4).1,3 commonly, nerves run along the same course as arteries, so often it is helpful to use color Doppler imaging to identify vascular However, some of the types of movements seen on US are more structures to ensure proper identification of nearby nerves. Muscle difficult to quantitate, (e.g., the degree of excursion of finger blood flow is a contributor to muscle volume as well.3 With even flexor tendons imaged in the sagittal view of the hand with flexion mild amounts of exercise, blood flow increases to muscle and this 10 CAPTURING MOTION WITH ULTRASOUND: BLOOD, MUSCLE, NEEDLE, NERVE blood flow can be detected in the median nerve at the wrist in some patients with , particularly those with larger cross sectional areas. The increased median nerve size, echogenicity, and vascularity seen in patients with CTS are N reduced by local steroid injections, suggesting a contributing role 18 T for vascularity in the pathogenesis of this disorder. In leprosy increased blood flow has been found in nerves particularly in T active stages of nerve infection.19-20 Blood flow has not been well studied in other inflammatory disorders of nerve, or even in more routine disorders such as diabetic neuropathy. More information is available on changes in blood flow in muscle disease,15-17 but, even here, the literature is scant.

Doppler Principles

Figure 5. This is a color flow Doppler sagittal image (shown here in black The Doppler Effect, in US, refers to a shift in the recorded sound and white) of the median nerve (N) at the wrist during slow flexion of the frequency of an echo caused by either motion of the sound source, fingers (distal is to the left). Note the color Doppler enhances the flexor sound receiver (in this case the US transducer), or the reflector. In tendons (T) as they move towards the transducer (red on the color plate), clinical US, the moving reflector is almost always blood, but lately but does not enhance over the nerve, which moves at a much slower rate there has been some interest in measuring cardiac wall motion and its colorization is blocked by the wall filter intrinsic to most color flow with US. If the sound source is approaching the transducer, the Doppler displays. Doppler Effect leads to an increase in the cycles per second of reflected sound waves compared to a stationary source, andif the sound source is moving away from the transducer, there is a corresponding decrease in the cycles per second of the reflected sound waves. The shift in frequency, in fact, is directly proportional to the speed of the source (or of blood flow), so the relationship, when expressed graphically, or acoustically, is intuitive. Of particular convenience is the fact that Doppler shifts with blood T flow, given that the frequency of US and speed of blood flow (or N T some types of tissue movement) occur in the audible frequency range (e.g., 1.3-20 kHz).2,6 The direct acoustic feedback of the Doppler shift makes it quite compelling to sonographers.

Traditional color flow Doppler imaging presents a color-coded display of the average blood flow speed (Doppler shift) and direction at each point in the image. This type of presentation, which is influenced by the angle of the transducer relative to blood flow, is useful for analyzing flow characteristics peculiar to blood vessels (eddies, reversal of flow in aortic regurgitation, etc.). However, because it only displays mean blood flow, it uses only a relatively small portion of the available information Figure 6. This is the same view as Figure 5 (shown here in black and to create the display.2,6 Color flow Doppler displays use a wall white), but this time the fingers are flexed rapidly, and the nerve moves function, or a low-frequency shift filter, which eliminates all the a bit more briskly. This is why both the nerve (N) and the tendons (T) distracting effects of relatively high amplitude but low-frequency enhance (red on the color plate). The presence of a wall filter blocks the movement information that comes from cardiac and blood vessel colorization of structures that move too slowly. wall movement. Color flow Doppler can also be used to image R = radial head tendon movement (Fig 5 and 6). For those interested in looking at the movements of muscle, the presence of such a wall filter significantly impairs the ability of the instrument to detect muscle can even lead to measurable increases in muscle dimensions.8 With movement. powerful contractions of muscle, intramuscular pressure exceeds that of arterial and venous pressure, so overall muscle volume may Power Doppler imaging, unlike color flow Doppler, uses the decrease slightly with vigorous contraction; this finding also has area under the curve of all that moves in the display (instead of implications for the ability of muscle to maintain peak contraction mean frequency of Doppler shift calculated from a background over time, before it needs to switch to anaerobic metabolism. of varying frequencies), regardless of the variations in moving However, changes in blood flow also may indicate the presence speeds and therefore produces a more robust and less noisy signal. of disease. Increased muscle blood flow has been described in However, the display lacks directionality and speed information.2,6 patients with inflammatory muscle disease.15-17 Changes in other As a result, when demonstrating blood flow distribution, or in muscle diseases have not been well studied, if at all. Increased detecting slow rates of blood flow (where Doppler shifts are quite 11 BASIC PRINCIPLES OF IMAGING MOVEMENT WITH ULTRASOUND small), power Doppler imaging is superior to color flow Doppler. only one study that used US contrast agents to study nerve, and that Of course, power Doppler also displays low frequency movements was in healthy rabbit sciatic nerve, demonstrating the feasibility associated with breathing or muscle contraction, so its value is of using this approach in humans.22 diminished in proximal areas close to the heart or in the trunk if the patient is unable to control breathing. Conclusions

It is important to know that when performing power or color • There is a tension in US display between spatial and temporal Doppler imaging, the probe needs to produce about five times as resolution, such that better spatial resolution often reduces many pulses per second as it does during routine diagnostic US. temporal resolution and vice versa. As a rule, instruments are The duty factor (the percentage of time in which US is in the designed to favor spatial resolution. Awareness of this tension transmit mode) with color Doppler imaging ranges from 0.5% to and the instrumentation that governs spatial and temporal 5%, which significantly increases the thermal effects of scanning. display (particularly X-resolution features, averaging, Because much insonated sound energy is absorbed, US does tend persistence, and number of focal zones) is essential for to warm tissue.2,6 In general, the small degree of heating does optimizing the usefulness of the US examination. not pose safety risks (although special precautions are warranted • For precise measures of movement of muscle, M-mode for ocular scanning), but the user should be aware of how the imaging, which is generally relegated to certain types of instrument may affect patients. blood flow studies, is a useful option. • Color and power Doppler imaging use the Doppler Effect to Contrast Agents display, in a semiquantifiable fashion, movement of particles in blood or of tissue. The presence of a wall filter (which The development of contrast agents for US has lagged considerably minimizes the impact of cardiac wall motion when imaging behind the development of such agents for CT and MR, particularly blood flow in the heart) limits the ability of these techniques in the United States. Routine use of these agents currently is far to image muscle movement. more common in Europe.2,6 Unlike CT and MR counterparts, • Power Doppler imaging is most useful for detecting slow however, US contrast agents do not leak into surrounding rates of blood flow in inflammatory conditions of nerve or tissues, but remain intravascular. This is because they consist of muscle because it is more sensitive to total blood flow and microbubbles, with a protein or lipid shell. Because of their defined has less noise than color flow Doppler. Color flow Doppler geometry, bubbles have an internal resonant frequency that can imaging is useful for imaging flow in large blood vessels and be induced by sound or thermal energy. This latter property was interrogating structures, such as cysts, that may be atypical discovered by Lord Rayleigh a century ago, who began studying vascular anomalies. this phenomenon in order to better understand the unusual acoustic • Contrast enhanced US is an exciting new technology that can properties of water as it is brought to a boil in a teapot.2121 When provide enhanced diagnostic and therapeutic opportunities in excited by low-intensity US, their internal resonant frequency sets the assessment of nerve and muscle disease; further clinical them to oscillating and releasing frequencies that are harmonics study is warranted. of the excitation frequency of routine US. As such, highly selective focusing at harmonic frequencies on the receptive side References can provide selective imaging of the presence of microbubbles.21 Most routine blood flow in tissues and organs is invisible because 1. Walker FO, Cartwright MS, eds. Neuromuscular ultrasound. the flow is too slow to be identified by power Doppler imaging, Philadelphia: Elsevier/Saunders; 2011. and microbubble technology, therefore, permits visualization of 2. Kremkau FW. Sonography: principles and instrumentation. the vascular supply with far more sensitivity and detail than is Philadelphia: Elsevier/Saunders; 2011. available without it. 3. Walker FO. Neuromuscular ultrasound. Neurol Clin 2004;22:563- 590. Ligands can be attached to microbubbles, making them anatomic 4. Walker FO. Basic principles of ultrasound. In: AANEM Course biomarkers, and, in animal models, such ligands can be used to Handout: Ultrasound. Rochester, MN: American Association of identify intravascular antibodies/antigens in ways not possible Neuromuscular & Electrodiagnostic Medicine; 2010. with soluble contrast agents used in MR and CT. For example, 5. Walker FO. Basic principles of ultrasound. In: Walker FO, using small animal transducers (40 MHz) and microbubbles tagged Cartwright MS, eds. Neuromuscular ultrasound. Philadelphia: with antibodies that recognize endothelial growth factor receptor Elsevier/Saunders; 2011. pp 1-23. II, melanoma nodules can be identified in mice by US imaging 6. Brandt WE. The core curriculum: ultrasound. Philadelphia: of retained microbubbles in their vascular supply.21 Microbubbles Lippincott, Williams & Wilkins; 2001. also can be used with targeted high-intensity focused US therapy 7. Walker FO. Normal neuromuscular sonography. In: Tegeler CH, to help disrupt endothelial and blood brain barriers to enhance Babikian VL, Gomez CR, eds. Neurosonology, 1st ed. New York: absorption of systemically administered pharmacotherapy. Of Mosby-Year-Book; 1996. pp 397-405. great interest, microbubbles, which are disrupted at the site of 8. Walker FO. Assessing muscle function at the bedside: can we do high intensity US, also can be used in animal models to transport better? Muscle Nerve 2010:42(4):530-538. therapeutic agents, and even viruses, which are then selectively 9. Delaney S, Worlsey P, Warner M, et al. Assessing contractile ability delivered to target areas.21 However, much of this technology is of the quadriceps muscle using ultrasound imaging. Muscle Nerve still in its initial exploratory phases; at this time, there has been 2010;42:530-538.

12 CAPTURING MOTION WITH ULTRASOUND: BLOOD, MUSCLE, NEEDLE, NERVE

10. Walker FO, Cartwright MS. Neuromuscular ultrasound as a com- 16. Meng C, Adler R, Peterson M, et al. Combined use of power Doppler plement to electrodiagnosis. In: Aminoff M, ed. Electrodiagnosis and gray-scale sonography: a new technique for the assessment of in clinical neurology. New York: Elsevier/Churchill Livingstone; inflammatory myopathy. J Rheumatol 2001;28:1271-1282. in press. 17. Shook SJ. Ultrasound in inflammatory myopathies. In: Walker 11. Walker FO, Harpold JG, Donofrio PD, Ferrell WG. Sonographic FO, Cartwright MS, eds. Neuromuscular ultrasound. Philadelphia: imaging of muscle contraction and fasciculations: a comparison Elsevier/Saunders; 2011. pp 125-131. with electromyography. Muscle Nerve 1990;13:33-39. 18. Cartwright MS, White DL, DeMar S, Wiesler E, Sarlikiotis T, 12. Yoshii Y, Villarraga HR, Henderson J, et al. Ultrasound assessment Chloros GD, Yoon JS, Won JS, Molnar JA, DeFranzo AJ, Walker of the displacement and deformation of the median nerve in the FO. Median nerve changes following steroid injection for carpal huma carpal tunnel with active finger motion. J Bone Joint Surg tunnel syndrome. Muscle Nerve 2011;44:25-29. Am 2009;91:2922-2930. 19. Elias J Jr., Nogueira-Barbosa MH, Feltrin Lt, et al. Role of ulnar 13. Oh S, Belchlavek M, Zhao C, et al. Detection of differential gliding nerve sonography in leprosy neuropathy with electrophysiologic characteristics of the flexor digitorum superficialis tendon and correlation. J Ultrasound Med 2009;28:1201-1209. subsynovial connective tissue using color Doppler sonographic 20. Marinoli C, Derchi LE, Bertolotto M, et al. US and MR imaging of imaging. J Ultrasound Med 2007;26:149-155. peripheral nerves in leprosy. Skeletal Radiol 2000;29:142-150. 14. Hough AD, Moore AP, Jones MP. Reduced longitudinal excursion 21. Wilson SR, Burns PN. Microbubble-enhanced US in body imaging: of the median nerve in carpal tunnel syndrome. Arch Phys Med what role? Radiology 2010;257:24-39. Rehabil 2007;88:569-576. 22. Wang Y, Tang P, Zhang L, et al. Quantitative evaluation of the 15. Weber MA, Jappe U, Kasig M, et al. Contrast-enhanced ultrasound peripheral nerve blood perfusion with high frequency contrast- in dermatosmyositis and polymyositis. J Neurol 2006;253:1625- enhanced ultrasound. Acad Radiol 2010;17:1492-1497. 1632.

13 14 Ultrasound and Blood Flow Imaging in the Diagnosis of Entrapment Neuropathy Einar P. Wilder-Smith, MD, DTM&H Professor, Division of Neurology Director, Neurology Diagnostic Laboratory National University Singapore Singapore

Senior Consultant, Spinal Injury Centre University Hospital Heidelberg Heidelberg, Germany

Introduction epineurium loosely connects to the perineurium and facilitates the sliding of one fascicle independent to an adjacent fascicle.3 Part Ultrasound (US) has undergone major technical innovations of the function of the epineural connective tissue is to facilitate over the last decade and now is firmly established as a diagnostic the dispersion of external compressive forces.4 Connective tissue technique in the investigation of peripheral nerve disease.1 It can within nerve fascicles is termed endoneurium (Fig. 1). The accurately depict both structural nerve changes as well as provide amount and distribution of connective tissue within nerves varies, information on nerve blood flow. Because both the structure and probably to accommodate for varying strains and stresses directed blood flow to nerves are altered in nerve entrapment syndromes, at different parts of the nerve. US can be particularly helpful in their investigation and diagnosis. Although magnetic resonance imaging also can be useful in the examination of peripheral nerves, it lacks the resolution of US and is not well suited to routine use.2 This discussion will focus on the changes that occur in chronic nerve entrapment syndromes and how these can be detected by US. Carpal tunnel syndrome (CTS), being the most common and best studied entrapment neuropathy, will be considered in the main. To understand how a nerve reacts EV to compression, it is helpful to first consider the microanatomy of a nerve. This will be followed by considering the changes that Ep occur both in structure and vascularization in a peripheral nerve Axons in reaction to chronic pressure. IFV

Nerve Anatomy P The basic constituents of a nerve—numerous myelinated and nonmyelinated nerve fibers running in a parallel longitudinal plane—are organized into discrete bundles, called fascicles, by Figure 1. Microanatomy of a peripheral nerve. a tough encircling membrane, the perineurium. The fascicles are EV = epineural venule, IFV = interfascicular venule, P = perineurium, loosely bound by connective tissue, the epineurium. Interfascicular Ep = epineurium 15 Ultrasound and Blood Flow Imaging in the Diagnosis of Entrapment Neuropathy The basic constituents of a peripheral nerve can be identified with US machines in good detail using 10 MHz and greater probes. In general, a normal nerve can be distinguished from the surrounding tissue by being more echogenic (darker) than muscle but less echogenic than tendons. A nerve visualized longitudinally shows the darker tubular fascicles surrounded by the whiter peri/epineurium. Viewed in transverse cuts, this gives rise to the characteristic “honeycomb structure” by which nerves are typified.5

Peripheral nerves have a rich blood supply. The nutrient vessels for the median nerve are derived from both the ulnar and radial artery and feed into a rich epineural, inter-, and intrafascicular vascular plexus where abundant anastomosing occurs. Two levels of capillary plexus can be identified.6 Towards the surface of the nerve lies the epineural capillary plexus and more internally is the perifascicular capillary plexus. Both are supplied and drained by corresponding arteries and veins and both systems are intricately connected by anastomosis.6 The predominant arrangement of the vessels is in a longitudinal direction.6 This is easily apparent when performing Doppler US of the median nerve (Fig. 2). The surface epineurium is drained by both the superficial and the deep venous system, possibly to prevent venous engorgement from external compression. Some nerves in areas more exposed to external pressure (e.g., the median nerve at the carpal tunnel) are highly fascicular and in these regions demonstrate multiple large interfascicular vessels. Nerves composed of a single fascicle (e.g., the ulnar nerve at the sulcus ulnaris) have superficially placed nutrient arteries, resulting in more vulnerability to ischemia from external pressure.4

Peripheral Nerve Vascular Changes Resulting From Chronic Figure 2. Median nerve blood flow in a patient with typical carpal tunnel External Pressure syndrome. From top to bottom, each picture represents sequential frames taken from a video recording. Chronically compressed nerves respond by enlarging. The hour R Med = right median nerve glass-like median nerve changes in CTS, first described by Pierre Marie and Charles Foix in 1913, summarize the changes occurring in chronic nerve entrapments. Typically, the increase in nerve size occurs just proximal (1-2 cm) and—to a lesser extent—distal to the site of compression (Fig. 3).2 In CTS, the cross-sectional nerve area of the median nerve is characteristically increased at the distal wrist crease at the edge of the proximal flexor retinaculum and also to a lesser degree at its distal region.7

TL Elevated extraneural pressure rapidly interferes with intraneural microvascular blood flow, axonal transport, and nerve function. MN Early changes include endoneurial and subperineurial edema with displacement of myelin and combined with signs of inflammation. Animal models of CTS show that the earliest median nerve reaction to entrapment is increased Schwann cell turnover in the face of preserved conduction.8 The subsequently vigorous proliferation of endoneurial fibroblasts and capillary endothelial cells followed by fibrosis with development of sheets of fibrous tissue results in nerve enlargement and increased vascularity.8 Figure 3. Typical nerve enlargement in median nerve entrapment at the wrist. On US, enlarged nerves (due to entrapment) are less echogenic5,9 MN = median nerve, TL = transverse ligament, swelling = nerve enlargement and in the case of CTS have an increased vascularity proximal proximal and distal to the compression by the TL to the site of compression demonstrable with power Doppler imaging.10 The technique and measurement of the cross-sectional 16 CAPTURING MOTION WITH ULTRASOUND: BLOOD, MUSCLE, NEEDLE, NERVE area of the median nerve at the carpal tunnel inlet takes only a and angiogenesis by binding to the fetal liver kinase 1 (Flk-1) few minutes to learn and has good inter- and intra-observer receptor of endothelial cells and initiates the protein kinase- reliability.7 signaling cascade.21

There is good evidence now that in patients with a clinical Two recent publications have suggested that detecting median diagnosis of CTS, sensitivity and specificity of the cross-sectional nerve blood flow proximal to the site of compression via color area of the median nerve at the carpal tunnel inlet (os pisiform Doppler is of value in the diagnosis of CTS.22,23 However, judging level) on US is the same as that for a nerve conduction study by the rapidity of technological improvement of US, it would (NCS).15 Three other sonographical features have also been seem that whether or not blood supply of a nerve can be shown used to diagnose CTS: (1) the ratio of the cross-sectional area is dependent mainly on the technical characteristics of the US (at pisiform bone) and the cross-sectional area at the level of the employed.24 With enhanced detection of nerve blood flow, in the distal radius (also termed swelling ratio); (2) the flattening ratio future it may become possible to directly show nerve ischemia at the level of the hook of hamate; and (3) palmar bowing of the at the site of compression. In the author’s study of median nerve flexor retinaculum. A review of the literature found that the most vascularity in patients with CTS (submitted for publication), reliable US parameter is an increase in the cross-sectional area of quantifying median nerve vascularity by measuring blood flow the median nerve at the level of the pisiform bone.11 Studies have velocity was explored. Those with clinically highly-likely CTS also established the correlation of median nerve cross sectional had significantly higher blood flow velocity than those with area with NCSs,12 motor unit number estimation13 and clinical clinically indeterminate CTS and those without symptoms. Figure severity.14 3 shows enhanced median nerve blood flow demonstrated by color Doppler in a patient with CTS. However, one still needs to be mindful that patients with negative US imaging can have a positive NCS and visa versa. However, measuring blood flow velocity alone likely is not a representative parameter of the altered vascular state of the Until recently, the impact of the naturally differing size of the entrapped median nerve. The further developments of color median nerve between individuals has been neglected. An Doppler for the diagnosis of entrapment neuropathies will need important study (that may well lead to more standardized outcomes to address what indices best distinguish normal from abnormal of sonographic results) has devised a formula incorporating the nerve blood flow. wrist circumference to counter for the effect of the naturally varying size of the median nerve in the diagnosis of CTS.16 In an attempt to do so, a composite derived score for median Similar to temperature measurements in NCSs, wrist size should nerve vascular abnormality was developed based on the estimated be accounted for in standard US examinations. percentage area of blood flow within the nerve and its consistency as well as location of flow.25 Future studies characterizing A potentially interesting advance in the use of US for the abnormal nerve blood flow also will need to address vasomotion, detection of structural nerve damage is the development of a phenomenon dependent on sympathetic drive which induces objective measurements of nerve density. Nerve density uses changes of blood flow over time.26 Because several factors grey scale analysis to measure a composite score of the combined influence vasomotion, careful control of autonomic influences hypoechoic and hyperechoic areas of peripheral nerves, and it has combined with prolonged recording and possibly provocating recently been used to discriminate between patients with mild and maneuvers may need to be implemented. severe CTS.17 This technique uses simple software to eliminate the problem of subjective assessment of varying degrees of nerve Conclusion edema. As stated earlier, this discussion has centered on the investigation Peripheral Nerve Vascular Changes of median nerve entrapment in CTS. Many other nerve Resulting From Chronic entrapments are amenable to US diagnosis by using increased Nerve Pressure nerve cross sectional area proximal to the site of compression. Nerve entrapments that have been assessed include the ulnar, Animal studies show that, initially, chronic nerve compression radial, peroneal sciatic, posterior tibial, and the lateral femoral results in nerve ischemia at the site of compression.18 Proximal to cutaneous nerves. Little is known about the nerve vascular status the site of compression, animal models show augmented numbers in these nerve entrapments. of blood vessels18 and perioperative findings of CTS patients reveal increased median nerve vascularity on macroscopic References inspection.19,20 The exact pathophysiological basis of the increased neural vascularity at the proximal carpal tunnel in chronic median 1. Padua L, Martinoli. From square to cube: ultrasound as a nerve entrapment is not well known. Compensatory vascularity natural complement of neurophysiology. Clin Neurophysiol in response to chronic hypoxia may be a result of increased 2008;119:1217-1218. expression of vascular endothelial growth factors. This has been 2. Walker F, Cartwright MS. Neuromuscular ultrasound: emerging demonstrated in models of chronic nerve compression in adult from the twilight. Muscle Nerve 2011;43:777-779. male Sprague-Dawley rats, with increased production of vascular 3. Millesi H, Zoch G, Reihsner R. Mechanical properties of peripheral endothelial growth factor (VEGF) messenger RNA proximal to nerves. Clin Orthop Relat Res 1995;314:76-83. the site of compression. VEGF induces blood vessel sprouting 17 Ultrasound and Blood Flow Imaging in the Diagnosis of Entrapment Neuropathy

4. Sunderland S. The connective tissues of peripheral nerves. Brain 16. Claes F, Meulstee J, Claessen-Oude Luttikhuis TT, Huygen PL, 1965;88:841-854. Verhagen WI. Usefulness of additional measurements of the median 5. Wilder-Smith E, Rajendran K, Therimadasamy AK. High-resolution nerve with ultrasonography. Neurol Sci 2010;31:721-725. ultrasonography for peripheral nerve diagnostics. A guide for 17. Tagliafico A, Tagliafico G, Martinoli C. Nerve density: anew clinicians involved in diagnosis and management of peripheral parameter to evaluate peripheral nerve pathology on ultrasound. nerve disorders. Singapore: World Scientific; 2010. pp 3-8. Preliminary study. Ultrasound Med Biol 2010;36:1588-1593. 6. Blunt MJ. The vascular anatomy of the median nerve in the forearm 18. Rydevik B, Lundborg G and Bagge U. Effects of graded compression and hand. J Anat 1959;93:15-22. on intraneural blood blow. An in vivo study on rabbit tibial nerve. 7. Nakamichi KI, Tachibana S. Enlarged median nerve in idiopathic J Hand Surg [Am] 1981;6:3-12. carpal tunnel syndrome. Muscle Nerve 2000;23:1713-1718. 19. Mackinnon SE, Dellon AL, Hudson AR and Hunter DA. Chronic 8. Gupta R, Steward O. Chronic nerve compression induces human nerve compression—a histologic assessment. Neuropathol concurrent apoptosis and proliferation of schwann cells. J Comp and Appl Neurobiol 1986;12:547-565. Neurol 2003;461:174-186. 20. Neary D, Ochoa J, Gilliatt RW. Sub-clinical entrapment neuropathy 9. Buchberger W. Radiologic imaging of the carpal tunnel. Eur J in man. J Neurol Sci 1975;24:283-298. Radiol 1997;25:112-117. 21. Gupta R, Gray M, Chao T, Bear D, Modafferi E, Mozaffar T. 10. Mallouhi A, Pulzl P, Trieb T, Piza H, Bodner G. Predictors of Schwann cells upregulate vascular endothelial growth factor carpal tunnel syndrome: accuracy of gray-scale and color Doppler secondary to chronic nerve compression injury. Muscle Nerve sonography. AmJ Roentgenol 2006;186:1240-1245. 2005;31:452-460. 11. Beekman R, Visser LH. Sonography in the diagnosis of carpal 22. Mallouhi A, Pulzl P, Trieb T. Predictors of carpal tunnel syndrome: tunnel syndrome: a critical review of the literature. Muscle Nerve accuracy of gray-scale and color Doppler sonography. Am J 2003;27:26-33. Roentgenol 2006;186:1240-1245. 12. Padua L, Pazzaglia C, Caliandro P, Granata G, Foschini M, 23. Ghasemi-Esfe AR, Khalilzadeh O, Mazloumi M. Combination of Briani C, Martinoli C. Carpal tunnel syndrome: ultrasound, high-resolution and color Doppler ultrasound in diagnosis of carpal neurophysiology, clinical and patient-oriented assessment. Clin tunnel syndrome. Acta Radiol 2011;52:191-197. Neurophysiol 2008;9:2064-2069. 24. Wilder-Smith EP. Combination of high-resolution and color 13. Bayrak IK, Bayrak AO, Tilki HE, Nural MS, Sunter T. Doppler ultrasound in diagnosis of carpal tunnel syndrome. Acta Ultrasonography in carpal tunnel syndrome: comparison with Radiol 2011; accepted for publication. electrophysiological stage and motor unit number estimate. Muscle 25. Ng WPK, Therimadasamy AK, Ng E, Wilder-Smith EP. Making Nerve 2007;35:344-348. Ultrasonography more effective for determining carpal tunnel 14. Karadağ YS, Karadağ O, Ciçekli E, Oztürk S, Kiraz S, Ozbakir syndrome—preliminary results of a study evaluating vascular S, Filippucci E, Grassi W. Severity of carpal tunnel syndrome abnormalities, morphology and neurophysiology of the median assessed with high frequency ultrasonography. Rheumatol Int nerve. Neurology 2011;76:A522-A523. 2010;30:761-765. 26. Kobayashi S, Mwaka ES, Meir A.Vasomotion of intraradicular 15. Visser LH, Smidt MH, Lee ML. High-resolution sonography microvessels in rat. Spine 2009;34:990-997. versus EMG in the diagnosis of carpal tunnel syndrome. J Neurol Neurosurg Psychiatry 2008;79:63-67.

18 Dynamic Ultrasound in the Assessment of Focal Neuropathies

Michael S. Cartwright, MD Assistant Professor of Neurology Wake Forest School of Medicine Winston-Salem, North Carolina

Introduction Median Mononeuropathy At The Wrist

High-resolution ultrasound (US) was first described for the Nerve Movement assessment of focal nerve disease in 1991, when Buchberger and colleagues outlined the ultrasonographic changes observed in the Prior to the development of high-resolution US transducers, median nerves of those with carpal tunnel syndrome (CTS).1 Since it was not known how much movement occurred in nerves in then, neuromuscular US has gained momentum as a diagnostic vivo during routine flexion of joints, and most clinicians and tool and complement to electrodiagnostic (EDX) studies for researchers assumed nerves only moved minimally. However, many neuromuscular conditions, including focal nerve disease. with the advent of neuromuscular US and the study of CTS, it Hundreds of articles have been published on neuromuscular US became clear that the median nerve at the wrist moved quite for CTS alone, and there have been many others written on ulnar extensively with routine flexion/extension of the fingers and wrist. neuropathy at the elbow and wrist, , fibular The first study to demonstrate and quantify this movement came neuropathy at the knee, and tibial neuropathy, among others. from Nakamichi and Tachibana in 1995.2 In this study the median US is an excellent imaging tool for focal nerve disease for many nerve at the wrist was imaged in the of 30 control subjects reasons. It is portable, easily accessible, painless, free of radiation, and 30 individuals with CTS, and the amount of movement of the precise, and it allows the examiner to focus on the small portion median nerve during full flexion and extension of the index finger of the nerve that may be affected. In addition, US allows for real- was quantified by a blinded rater by comparing the location of time imaging of structures, including structures in motion, which the nerve to the ulnar artery. In control subjects the nerve moved cannot be easily accomplished with other imaging modalities, freely, with an average displacement of 1.75 mm (SD 0.49 mm), such as magnetic resonance imaging. Most neuromuscular US whereas in those with CTS the median nerve showed restricted studies have focused on static anatomic changes seen in nerves movement with an average displacement of 0.37 mm (SD 0.34 affected by focal nerve disease, but there is a growing body of mm). This statistically significant (p=0.0001) difference can be literature discussing other findings detectable with US, including seen in Figure 1, and the study’s authors commented that this dynamic changes within and around focal nerve disease. finding was expected since surgeons often note that the median nerve is adhered to the flexor retinaculum during open carpal tunnel This discussion will cover the dynamic findings seen with US in release. Interestingly, very few studies have examined this finding the following focal neuropathies: median at the wrist, ulnar at the since the initial report in 1995. In this author’s electromyography elbow, and radial at the spiral groove. (EMG) laboratory at Wake Forest similar findings of decreased 19 Dynamic Ultrasound in the Assessment of Focal Neuropathies

Figure 2. Both images are cross-sectional views of the median nerve (arrows) at the wrist. In the left image, the wrist is in the neutral position and the median nerve is superficial to the flexor tendons. In the right image, the fingers and wrist are flexed and the median nerve is surrounded by the flexor tendons.

PATIENTS CONTROL SUBJECTS

Figure 1. The median nerve in those with carpal tunnel syndrome showed Figure 3. This image is of the carpal tunnel, with the fingers extended. significantly less transverse movement than in control subjects. With this movement, flexor digitorum muscle has entered the tunnel(star) From Nakamichi and Tachibana.2 and the muscles are adjacent to the median nerve (arrow). transverse movement of the median nerve in those with CTS have Muscle Movement been observed, but when this assessment is performed patients are asked to flex and extend all the fingers and the wrist simultaneously While clinicians and researchers initially were not aware (Fig. 2). Movement of the median nerve is graded as described in of the degree of nerve movement, it was intuitive prior to the Table, and this grade is then combined with other parameters the development of high-resolution US that muscles moved (i.e., median nerve cross-sectional area) to establish a diagnosis extensively during flexion and extension of joints. However, it of median mononeuropathy at the wrist. A recent study also again required the development of neuromuscular US to clarify shows that injection of steroids around the median nerve leads to that muscle enters into the carpal tunnel during routine movement statistically significant increases in median nerve mobility, which of the wrists and fingers, and muscle can even be present within correlate with clinical improvement.3 the tunnel with the wrist in the neutral position (Fig. 3). The lack of awareness of this phenomenon quickly becomes apparent with In addition to transverse movement, the median nerve also glides an internet image search of carpal tunnel schematics drawn over in a distal-proximal longitudinal plane with finger flexion and the years. Essentially none of the schematics show muscle within extension. This movement is easy to observe with US, but it the carpal tunnel, rather they just demonstrate the median nerve, can be challenging to measure. Hough and colleagues designed flexor tendons, bursa, and sometimes the synovium. Surgical case a custom upper limb support jig to stabilize the arm and then reports since the 1970s have described aberrant muscle within used Doppler to compare median nerve longitudinal excursion the carpal tunnel in some individuals undergoing release for in 18 individuals with CTS and 37 control subjects.4 Using a CTS,6 and those that routinely perform neuromuscular US will blinded study design they demonstrated a significant decrease note flexor digitorum and lumbrical muscle within the tunnel, in median nerve longitudinal excursion in those with CTS (8.3 both in those with CTS and those without. Flexion of the fingers mm) compared to control subjects (11.2 mm) with the elbow will often introduce even more lumbrical muscle into the tunnel, extended (p=0.013), but no significant difference when the elbow and extension of the fingers and wrist can introduce more flexor was flexed (p=0.089). They also compared movement of the digitorum muscle. median nerve to movement of the flexor digitorum superficialis tendons and showed decreased relative movement of the median Research into the potential relevance of muscle intrusion has nerve with the elbow extended and flexed (p<0.001). However, a just begun, but screening of 698 wrists of manual laborers similar study of 17 individuals with CTS and 19 control subjects demonstrated nearly 88% of all wrists had some degree of muscle failed to show a difference in longitudinal gliding of the median intrusion into the carpal tunnel with flexion and extension of the nerve in the forearm between the groups.5 Advanced techniques, fingers and wrist, and those with CTS had more muscle within such as those used by Hough and colleagues and frame-by-frame the tunnel than those without CTS (p=0.0007).7 The amount of analysis, may be able to better quantify longitudinal gliding of the muscle within the tunnel can be quantified with cross-sectional median nerve, but it does appear that median nerve movement in area measurements, and prospective, serial studies of this finding the longitudinal plane also is decreased in those with CTS. may shed light on the etiology of idiopathic CTS.

20 CAPTURING MOTION WITH ULTRASOUND: BLOOD, MUSCLE, NEEDLE, NERVE Ulnar Mononeuropathy At The Elbow Radial Mononeuropathy At The Spiral Groove Nerve Movement Compression of the as it passes through the spiral It has long been recognized that upon flexion of the elbow some groove is a well-established cause of entrapment neuropathy, and individuals have pronounced movement of the ulnar nerve, and some refer to it as Saturday Night Palsy as it has been described this has been postulated to be a cause of ulnar neuritis.8 In some, to occur after an evening of drinking and subsequent heavy sleep the ulnar nerve subluxes, meaning it moves medially out of the with the arm draped over a chair. Besides prolonged compression, ulnar groove and lies superficial to the medial epicondyle, but in other causes of radial mononeuropathy in the spiral groove have others the nerve completely dislocates, meaning it moves medially been described, and this author has reported a case in which and then passes over and eventually lies anterior to the medial dynamic ultrasonographic imaging of the radial nerve assisted in epicondyle. In many individuals subluxation and dislocation diagnosis and treatment planning.13 In this case, an individual was of the ulnar nerve during elbow flexion can be detected with shot in the arm and the humerus shattered. The patient immediately palpation, but in others, particularly those with thicker arms, the developed a dense radial neuropathy, but nerve conduction nerve cannot be palpated.

Because US can produce dynamic images, it is ideally suited for continuous imaging of the ulnar nerve throughout full flexion and extension of the elbow. In a study of 212 elbows with neuromuscular US, it was noted that subluxation occurred in 23.1% of elbows and full dislocation in 8.5%.9 While there are several case reports of individuals with at the elbow and ulnar nerve hypermobility noted with US, an increased rate of ulnar nerve subluxation or dislocation has not been reported in those with ulnar neuropathy at the elbow compared to control subjects. It has been noted in a study of 78 elbows that ulnar nerve displacement during elbow flexion results in a falsely increased calculated nerve conduction velocity by an average of 5.33 ms (SD 2.29 ms), which leads to false-negative results and may explain the relatively decreased sensitivity of nerve conduction studies (NCSs) for the diagnosis of ulnar neuropathy at the elbow.10 The ability to identify the site of maximal nerve enlargement and detect subluxation and dislocation, along with the suboptimal accuracy of NCSs for the condition, make neuromuscular US an excellent tool for the evaluation of ulnar neuropathy at the elbow, and further research in this field is encouraged.11

Snapping Triceps

Snapping triceps is a condition in which the medial head of the triceps muscle, which inserts on the olecranon process, snaps over the medial epicondyle during elbow flexion. When this occurs in combination with ulnar nerve subluxation or dislocation, irritation of the ulnar nerve can occur. Typical treatment of ulnar neuropathy at the elbow, with ulnar nerve transposition, often will not resolve the symptoms if a snapping triceps muscle is present. Ultrasonography of the ulnar nerve and triceps muscle and tendon in the posterior elbow can be performed as the patient flexes and extends the elbow. If the triceps tendon is displaced medially and anteriorly over the medial epicondyle during elbow flexion, then a snapping triceps is present. The true prevalence of this condition is not known, but case reports and series exist describing the condition and resolution of symptoms with appropriate surgical intervention focused on stabilizing and protecting both the ulnar Figure 4. A plain x-ray of the right humerus is shown (A), and the nerve and medial triceps.12 compound fracture can be observed with the bullet in the soft tissue. A cross-sectional ultrasound image at the level of fracture is shown (B). The radial nerve (dotted line) can be observed between the bone fragments of the fractured humerus (arrows). The cross-sectional area of the nerve is enlarged to 27 mm2 at this level. From Spinner and Goldner.12 21 Dynamic Ultrasound in the Assessment of Focal Neuropathies studies performed in the acute phase of the injury were unable dynamic imaging is needed, but there is already a solid literature to determine if the nerve was transected or if it remained intact base to currently support the use of dynamic ultrasonography in with a severe axonotmetic lesion. US of the radial nerve (Fig. 4) the assessment of focal mononeuropathies. demonstrated that it was located next to the shattered humerus, but a small portion of the nerve was poorly visualized because it REFERENCES was obscured by a bone fragment. Therefore, dynamic imaging of the radial nerve, with the patient repeatedly flexing and extending 1. Buchberger W, Schon G, Strasser K, Jungwirth W. High- the elbow, was performed. The proximal and distal portions of resolution ultrasonography of the carpal tunnel. J Ultrasound Med the nerve were observed to slide over the humerus during this 1991;10:531-537. movement, indicating that the nerve was intact through this 2. Nakamichi K, Tachibana S. Restricted motion of the median nerve segment. This finding resulted in conservative management and in carpal tunnel syndrome. J Hand Surg [Br] 1995;20:460-464. immediate surgical intervention was not pursued. Over the next 3 3. Cartwright MS, White DL, DeMar S., Wiesler ER, Sarlikiotis T, months his condition improved, with increased strength in radial Chloros GD, Yoon JS, Won SJ, Molnar JA, DeFranzo AJ, Walker nerve-innervated muscles. FO. Median nerve changes following steroid injection for carpal tunnel syndrome. Muscle Nerve 2011;44:25-29. This case demonstrates the utility of dynamic ultrasonographic 4. Hough AD, Moore AP, Jones MP. Reduced longitudinal excursion nerve imaging to confirm nerve anatomic continuity. This of the median nerve in carpal tunnel syndrome. Arch Phys Med principle can be applied to any nerve amenable to ultrasonographic Rehabil 2007;88:569-576. visualization and is particularly helpful in the acute evaluation of 5. Erel E, Dilley A, Greening J, Morris V, Cohen B, Lynn B. traumatic mononeuropathies. Longitudinal sliding of the median nerve in patients with carpal tunnel syndrome. J Hand Surg [Br ] 2003;28:439-443. Conclusions 6. Jackson DW, Harkins PD. An aberrant muscle belly of the abductor digiti quinti associated with median nerve paresthesias. Bull Hosp US is a powerful complement to EDX studies for the evaluation Joint Dis 1972;33:111-115. and diagnosis of focal mononeuropathies, and neuromuscular 7. Cartwright MS, Walker FO, Blocker JN, Schulz MR, Arcury US techniques continue to improve. In fact, a recent prospective TA, Quandt SA. Muscle intrusion into the tunnel in carpal tunnel blinded study of neuromuscular US in the assessment of focal syndrome. Muscle Nerve 10-1-2010. Abstract. nerve disease demonstrated that US modified the diagnostic and 8. Lazaro L III. Ulnar nerve instability: ulnar nerve injury due to therapeutic path in 42.3% of cases seen in an EMG laboratory, elbow flexion. South Med J 1977;70:36-40. leading the authors to conclude that “US should be used, whenever 9. Ozturk E, Sonmez G, Colak A, Sildiroglu HO, Mutlu H, Senol MG, possible, to improve assessment of nerve impairment.”14 The Basekim CC, Kizilkaya E. Sonographic appearances of the normal ability to easily perform dynamic studies is one of the great benefits ulnar nerve in the cubital tunnel. J Clin Ultrasound 2008;36:325- of imaging with US, and the detection of normal and abnormal 329. movements of nerve and muscle contribute to our ability to 10. Kim BJ, Date ES, Lee SH, Yoon JS, Hur SY, Kim SJ. Distance accurately diagnose focal nerve lesions. Further investigation into measure error induced by displacement of the ulnar nerve when the elbow is flexed. Arch Phys Med Rehabil 2005;86:809-812. 11. Walker FO, Cartwright MS. Neuromuscular ultrasound, 1st ed. Table Grading median nerve movement at the wrist Philadelphia: Elsevier; 2011. The patient is asked to repeatedly flex and extend the fingers and wrist 12. Spinner RJ, Goldner RD. Snapping of the medial head of the while the ultrasound transducer is held still. The grades described below triceps and recurrent dislocation of the ulnar nerve. Anatomical and are used to describe the degree of median nerve movement. dynamic factors. J Bone Joint Surg Am 1998;80:239-247. 13. Cartwright MS, Shik YJ, Ho LK, Deal N, Walker FO. Diagnostic ultrasound for traumatic radial neuropathy. Am J Phys Med Rehabil Description of nerve Grade Mobility assessment 2010; Epub ahead of print. movement 14. Padua L, Liotta G, Di PA, Granata G, Pazzaglia C, Caliandro P, The median nerve has Martinoli C. Contribution of ultrasound in the assessment of nerve 0 Decreased minimal movement in all diseases. Eur J Neurol 2011; Epub ahead of print. directions.

The median nerve moves 1 Slightly decreased freely in the transverse plane but does not dive deep.

The median nerve dives 2 Normal deep and is surrounded on all sides by the flexor tendons.

22 Ultrasound Imaging of the Diaphragm and as an Adjunct to Electrodiagnosis

Andrea J. Boon, MD, MBChB Assistant Professor Departments of Physical Medicine and Rehabilitation and Neurology Mayo Clinic College of Medicine Rochester, Minnesota

Ultrasound Imaging In The lies directly adjacent to the rectus femoris (femoral nerve/L2, L3, Electromyography L4 nerve roots); both muscles will activate with attempts at hip Laboratory Setting flexion. Similarly, the middle trapezius overlies the rhomboid muscle, and both muscles will contract with scapular retraction, Ultrasound (US) imaging provides excellent direct and real time although that is not the prime movement for the trapezius. The visualization of soft tissues. It provides details about anatomic two muscles have different innervation and if one is severely landmarks, fascial planes, and neurovascular structures adjacent atrophic, it may be difficult to identify with confidence in which to the intended target. With recent advances in technology, muscle the needle lies. high quality US machines are affordable and portable and they subsequently have become more widely available for a variety In cadavers, the accuracy of nonimage-guided needle placement of clinical applications. For the past several years, the author’s in the hands of experienced electrodiagnostic (EDX) physicians large, tertiary referral electromyography (EMG) laboratory has ranges from 0% to 83% depending on the muscle examined.1-3 gradually integrated the use of US imaging into a number of The author evaluated the accuracy of nonguided versus US- aspects of its daily clinical and academic practice. guided EMG needle placement in 14 separate muscles in the lower limb in unembalmed cadavers and found overall nonguided One of the most obvious indications for US in the EMG laboratory accuracy rates of 50% for a fully trained resident EDX physician setting is to ensure accurate muscle localization. A unique feature compared to 83% for an experienced staff EDX physician at a of US as compared to other imaging modalities is its ability to large academic EMG laboratory.4 With the use of US guidance, image both statically and dynamically. Muscles shorten and accuracy rates were markedly enhanced, with improvement to 96% thicken with contraction, which is easily appreciated through accuracy. Although cadaveric studies are limited by the lack of US. A muscle also can be passively flexed and extended while usual feedback (muscle insertional activity, motor unit activation, visualizing with US to allow accurate identification. and inability to palpate the contracting muscle), there are clinical parallels in which such feedback is not available. Examples Although clinicians are trained to use various techniques to include unresponsive or uncooperative patients, those with severe facilitate accurate localization during needle EMG (including denervation or spasticity preventing voluntary activation of the anatomic landmarks, palpation [during muscle activation], and muscle of interest, or the use of intramuscular wire electrodes proximity of motor unit firing with activation), there are clinical where immediate feedback is not possible. Muscle localization scenarios in which it can be challenging to isolate the exact muscle can also be challenging when the normal anatomy is altered by of interest. There are a number of muscles where inadvertent needle trauma, surgery, or obesity. placement in an adjacent muscle (with different peripheral nerve or nerve root innervation) will lead to an erroneous conclusion on In addition to improving accuracy, adjunctive US also may the part of the examiner. Some examples include the tensor fascia enhance the safety of needle EMG. US-guided needle examination lata muscle (superior gluteal nerve/L4, L5, S1 nerve roots) which can be utilized in higher risk situations such as the anticoagulated 23 Ultrasound Imaging of the Diaphragm and as an Adjunct to Electrodiagnosis include lack of central drive (such as in high spinal cord injury or encephalopathy), anterior horn cell or nerve root disease (at C3-C5 levels), polyneuropathy (including critical illness polyneuropathy and Guillain-Barré syndrome), myasthenia gravis or other disorders of neuromuscular transmission, myopathy (including critical illness myopathy), and phrenic neuropathy.

Needle EMG can provide important information regarding the underlying pathophysiology (e.g., differentiating between neuropathic, myopathic, and central disorders) as well as prognostic information regarding potential for meaningful recovery that may not be elicited on clinical grounds alone. Although the diaphragm Figure 1. Insertion points for diaphragmatic needle electromyography is an inherently high risk muscle to examine due to nearby vital examination are marked by an X. The needle is inserted just above the structures (i.e., liver, spleen, colon, and lung), when performed costal margin between the medial clavicular line and the anterior axillary with appropriate technique, the real risk actually appears to be line. The needle is inserted as far medially and caudally within the chosen quite low. interspace as possible and the lowest interspace that can be entered is targeted. Technique

Several techniques for needle examination of the diaphragm have been described.9,10 However, the technique described by Bolton has been shown to be the safest and most accurate.11-13 This technique involves needle insertion just above the costal margin at any interspace between the medial clavicular line and the anterior axillary line (Fig. 1). The interspace chosen is based on palpation and examiner preference, as in some cases cartilage may bridge the interspace, making needle insertion difficult, and another interspace must be chosen. The needle is inserted as far medially and caudally within the chosen interspace as possible. The angle of entry is perpendicular to the chest wall, with the needle passing first through skin and subcutaneous tissue before encountering the external oblique or rectus abdominus muscle, followed by external and internal intercostal muscles, and finally passing in to the diaphragm (Fig. 2).

At rest, the intercostal muscles should be fairly quiet; however, Figure 2. Anatomy of needle electromyography of the diaphragm. The they can be easily activated with vigorous inspiration, forced angle of needle entry is perpendicular to the chest wall, with the needle expiration such as coughing, or slight twisting of the chest wall. passing first through skin and subcutaneous tissue before encountering the Entry in to the diaphragm is signaled by bursts of motor unit external oblique or rectus abdominus muscle, followed by the intercostal potentials (MUPs) firing with each inspiration, and this can be muscles, and finally passing in to the diaphragm. The pleural reflection is accentuated by asking the patient to sniff quickly in through the usually at least 1.5 cm rostral to the lower costal margin. nose. Small redirections of the needle may be required to achieve complete entry of the needle in to the diaphragm; however, if motor units are initially heard to fire with inspiration but with patient, in which examination of certain muscles such as , further advancement of the needle motor units or spontaneous flexor pollicis longus, or posterior tibialis is necessary. Virtually activity are no longer audible, this suggests the diaphragm has all modern US machines have Doppler capability, which can be a been completely traversed and the needle should be withdrawn useful tool to identify nearby vascular structures that one should and redirected. MUPs in the diaphragm typically are shorter avoid.5,6 US also can be used for postprocedure surveillance duration, lower amplitude, and more numerous than MUPs in the after a high risk muscle has been needled or, when there has intercostal or limb muscles. been evidence of bleeding at the time of needle examination, to examine for a developing hematoma.7,8 Prior to attempting needle EMG of the diaphragm, it is prudent to discuss the potential risks with the patient, to obtain informed Needle Electromyography Of consent (either written informed consent or verbal consent The Diaphragm documented in the EMG report), and to instruct the patient to notify the EDX physician if they feel a deep aching or very sharp Needle EMG of the diaphragm is a useful electrophysiologic pain any time after the intercostal muscles have been entered, as technique in patients who present with unexplained dyspnea this may represent penetration of the pleura or peritoneum. or failure to wean from the ventilator. Underlying etiologies

24 CAPTURING MOTION WITH ULTRASOUND: BLOOD, MUSCLE, NEEDLE, NERVE Ultrasound-Guided Needle Electromyography of the Diaphragm Rationale

Needle EMG typically is performed without image guidance and although Bolton’s technique as described above is relatively safe and technically feasible, there is the potential for pneumothorax, penetration of abdominal viscera, and hemorrhage. Due to these risks, needle examination may be suboptimal, with failure to actually enter the diaphragm particularly in more challenging cases such as obese patients, patients with altered anatomy or advanced obstructive pulmonary disease in which the lungs are hyperinflated, and in cases of severe denervation or atrophy where there may be little muscle to target or lack of the usual auditory feedback to guide needle placement. In such cases, US guidance can enhance the safety and accuracy of the needle examination of the diaphragm.

Technique

US examination of the diaphragm can be performed easily at the bedside using a portable machine. Depending on the US system utilized, depths of up to 6 cm can be visualized using a linear probe at frequencies of 8-12 Hz. (In larger adults, a curvilinear transducer may be necessary to image the diaphragm at depths greater than 6-10 cm.) The seventh, eighth, and ninth ribs in the region of the anterior axillary line are identified, and the probe initially is placed perpendicular to the ribs, centered over the eighth intercostal space. Each rib is identified easily by the bright signal generated at the bony cortex and the acoustic shadowing deep to it. Subcutaneous tissue lies superficial to the ribs, and two layers of intercostal muscle bridge the space between any two adjacent ribs. Deep to the ribs, the diaphragm can be visualized (Fig. 3A).

The muscle layers are recognized easily by their location and ap- pearance. Longitudinally, muscles have a mixed echogenic ap- pearance, consisting of hypoechoic (dark) muscle fibers sepa- rated by hyperechoic (bright) fibroadipose septae (perimysium). Transversely, the mixed echogenicity pattern of muscle produces Figure 3. Ultrasound (US)-guided needle examination of the diaphragm. a “starry night” appearance. The diaphragm typically is identified (A) The transducer initially is placed perpendicular to the ribs and the by its deep location, curved geometry, and muscular echotexture. separate layers of tissue are identified: subcutaneous tissue (SC), two In addition, the diaphragm will thicken during inspiration as a layers of intercostal muscles (IC) spanning the ribs, diaphragm (D), and result of muscular contraction unless severely atrophic, in which pleura/lung (P) which is just coming into the field of view with inspiration.(B) case it will appear as a very thin layer of muscle (often only 1 mm The transducer is then aligned parallel to the ribs, overlying the intercostal thick) beneath the intercostal muscles and may not thicken with space. As the patient takes a deep inspiration, the bright shadow of the inspiration. lung is seen coming into the field of view from the superolateral direction, displacing the diaphragm and underlying liver. (C) The needle is inserted In the region of the lower intercostal spaces, the liver on the right parallel to the long axis of the transducer under real time US guidance until and the spleen on the left can be visualized deep to the diaphragm the needle tip (arrow) enters the diaphragm. The left side of the image is and appear as homogeneous, low intensity structures punctuated cephalad. by occasional blood vessels (Fig. 3). However, when the patient inhales deeply the lung will enter in to the field of view; the lung will appear as a bright high intensity shadow coming in from above and displacing the diaphragm and the underlying liver or spleen (Fig. 3B).

25 Ultrasound Imaging of the Diaphragm and as an Adjunct to Electrodiagnosis After initial identification of the anatomy perpendicular to the long muscle is contracting with inspiration and evaluate the quality of axis of the ribs, the transducer is then turned parallel to the ribs movement, including the presence of paradoxical motion. In cases overlying the intercostal space. At the author’s EMG laboratory, of respiratory failure, observation of the diaphragm with US while the seventh intercostal space typically will be evaluated initially, the phrenic nerve is stimulated at the supraclavicular fossa can be but other spaces will be subsequently evaluated as necessary to used to determine whether the recorded response truly represents identify the space providing the best visualization of the diaphragm, a diaphragmatic compound muscle action potential or merely where the muscle is thickest, with minimal encroachment of the a volume conducted response from nearby chest wall muscles. pleural space and or lung. The more posterior the probe is, the Transient discontinuation of mechanical ventilation under US higher the likelihood that lung will enter in to the field of view. observation can be performed to determine whether there is any Under real time US guidance, the needle can be inserted either spontaneous activation in cases of severe respiratory failure.7 parallel or perpendicular to the long axis of the transducer. At Normal values for diaphragm muscle thickness at end inspiration the author’s laboratory, the preference is to insert the needle and expiration currently are not available but even qualitatively parallel to the transducer (long axis approach), providing direct abnormalities are often quite apparent, particularly in unilateral visualization of the needle throughout the examination (Fig. cases where the patient can serve as their own control subject. 3B), while simultaneously monitoring the lung descending in to the field of view as the patient takes in a deep inspiration. The Ultrasound-Guided Needle scanning depth and transducer frequency should be adjusted to Electromyography Of Other Muscles allow the highest frequency to be used that will allow visualization at a sufficient depth to see the diaphragm. If a short axis approach The greatest concern when performing needle EMG of the is used, caution must be exercised to stop advancing the needle diaphragm is pneumothorax. In practice, the relative risk of this as soon as the bright tip of the needle is identified on US, as the complication is very low. In fact, pneumothorax is more likely needle tip and the shaft (i.e., the tip has moved beyond the plane to occur as a complication of needle examination of chest wall of the US beam) appear nearly indistinguishable. muscles such as the serratus anterior, rhomboid, and thoracic paraspinal muscles.14-16 US similarly can be used to localize Applications these muscles, particularly in obese subjects where ribs and other anatomic landmarks cannot be palpated. Image guidance ensures At the author’s EMG laboratory, US now is utilized on a accurate identification of the target muscle (since chest wall regular basis when examining the diaphragm. Even in relatively muscles are often difficult to activate in isolation, particularly straightforward cases, US easily can identify the rib space when weak), and allows qualitative evaluation for atrophy or signs that provides the best view of the diaphragm without lung of denervation in cases where needle examination is technically encroachment. In addition, the depth of needle penetration difficult or contraindicated (Fig. 4). In unilateral disease, the necessary to reach the diaphragm can be gauged quickly. Thus, patient can serve as their own control subject with comparison to if one is using a standard nonguided technique as described by the contralateral side. Bolton,11 with needle insertion perpendicular to the skin/chest wall (Fig. 2), knowing the anticipated depth of the diaphragm is US can be utilized to enhance the accuracy of needle EMG of helpful. any muscle that is not obscured by bone or too deep to visualize; in the vast majority of cases, US guidance is not necessary to In more difficult patients, direct visualization of the needle with accurately target muscles, but the author has found it very useful US throughout the insertion can minimize risk and maximize the to have US available for occasional, challenging situations that chance of entering the diaphragm. It is particularly helpful in more one runs across from time to time in an EMG practice. Some challenging cases, such as larger patients where ribs may be more difficult to palpate, patients with altered anatomy where landmarks cannot be relied upon for accurate guidance, patients with chronic obstructive pulmonary disease and associated hyperinflation of the lungs, patients on anticoagulation or with coagulopathy who would otherwise not be candidates for needle examination, and patients with severe atrophy or denervation of the diaphragm where the normal sound of motor unit potential firing can not be relied upon to guide needle placement. In such cases, use of an oblique “stand off” technique—where gel is heaped up beneath one end of the transducer to maintain a more perpendicular Figure 4. Example of ultrasound (US) application in needle relationship between the needle and the ultrasound beam when a electromyography (EMG) of chest wall muscles. The patient presented with steep approach is required to reach the muscle—can significantly winging of the scapula. Needle EMG showed no insertional activity and enhance needle visualization throughout the procedure.5,6 no motor unit activation, leading the electrodiagnostic physician to believe that they may not have entered the muscle, despite having placed the US imaging not only provides information on the proximity of needle down to bone. Therefore, an US examination was performed and nearby vital structures but also allows the EDX physician to demonstrated an atrophic, neurogenic (homogeneous) appearing serratus assess the quality and degree of motion of the diaphragm, both anterior muscle on the right, with a healthy appearing serratus anterior with respiration and in response to phrenic nerve stimulation. By muscle on the left, which is almost twice as thick and has the typical “starry visualizing the diaphragm in real time, one can determine if the night” heterogenous appearance of normal muscle on US. 26 CAPTURING MOTION WITH ULTRASOUND: BLOOD, MUSCLE, NEEDLE, NERVE examples include localization of a transposed flexor carpi ulnaris 4. Boon AJ, Oney-Marlow TM, Murthy NS, Harper CM, McNamara muscle; localization of the flexor pollicis longus muscle after five TR, Smith J. Accuracy of EMG needle placement in cadavers: non- prior surgeries on that muscle; localization of pronator quadratus guided versus ultrasound guided. Muscle Nerve 2011;44(1):45-49. in a severe anterior interosseous nerve injury after the muscle 5. Smith J, Finnoff JT. Diagnostic and interventional musculoskeletal could not be located on initial needle EMG; examination of the ultrasound: part 2. Clinical applications. Pm R 2009;1:162-177. iliopsoas muscle in an anticoagulated, obese patient with acute hip 6. Smith J, Finnoff JT. Diagnostic and interventional musculoskeletal flexor weakness; localization of the in a patient ultrasound: part 1. Fundamentals. Pm R 2009;1:64-75. with tibial neuropathy (as requested by the referring surgeon); 7. Boon AJ, Alsharif KI, Harper CM, Smith J. Ultrasound-guided localization of the median innervated portion of flexor digitorum needle EMG of the diaphragm: technique description and case profundus when the patient was too weak to selectively activate; report. Muscle Nerve 2008;38:1623-1626. and differentiation of a transplanted gracilis free muscle transfer 8. Lynch S, Boon A, Smith J, Harper C, Tanaka E. Complications from the underlying biceps and brachialis muscles in a patient of needle electromyography: hematoma risk and correlation status post brachial plexus reconstructive surgery. with anticoagulation and antiplatelet therapy. Muscle Nerve 2008;38:1225-1230. Conclusion 9. Goodgold J. Anatomical correlates of clinical electromyography, 2nd ed. Baltimore: Williams & Wilkins; 1984. p. 41. As US becomes an affordable, practical imaging modality that 10. Saadeh PB, Crisafulli CF, Sosner J, Wolf E. Needle electromyography is portable and easily incorporated in to the clinical setting, the of the diaphragm: a new technique. Muscle Nerve 1993;16:15-20. adjunctive use of US during the needle EMG examination should 11. Bolton CF, Grand’Maison F, Parkes A, Shkrum M. Needle be considered in certain challenging cases, when available. The electromyography of the diaphragm. Muscle Nerve 1992;15:678- necessary needle guidance skills can be acquired fairly quickly. 681. With appropriate training and with an indepth knowledge of 12. Chiodo A, Goodmurphy C, Haig A. Diaphragm needle placement neuroanatomy (a prerequisite for EDX physicians) combined techniques evaluated in cadaveric specimens. Arch Phys Med with the dynamic aspect of US, the identification of individual Rehabil 2006;87:1150-1152. muscles becomes relatively simple. It is anticipated that the use of 13. Koepke GH, Smith EM, Murphy AJ, Dickinson DG. Sequence of US in the needle EMG laboratory setting will continue to evolve action of the diaphragm and intercostal muscles during respiration. as the technology becomes more widespread. I. Inspiration. Arch Phys Med Rehabil 1958;39:426-430. 14. Honet JE, Honet JC, Cascade P. Pneumothorax after electromyographic electrode insertion in the paracervical muscles: REFERENCES case report and radiographic analysis. Arch Phys Med Rehabil 1986;67:601-603. 1. Chiodo A, Goodmurphy C, Haig A. Cadaveric study of methods 15. Miller J. Pneumothorax. Complication of needle EMG of thoracic for subscapularis muscle needle insertion. Am J Phys Med Rehabil wall. N J Med 1990;87:653. 2005;84:662-665. 16. Reinstein L, Twardzik FG, Mech KF, Jr. Pneumothorax: a 2. Chiodo A, Goodmurphy C, Haig A. Cadaver evaluation of EMG complication of needle electromyography of the supraspinatus needle insertion techniques used to target muscles of the thorax. muscle. Arch Phys Med Rehabil 1987;68:561-562. Spine 2006;31:E241-E243. 3. Haig AJ, Goodmurphy CW, Harris AR, Ruiz AP, Etemad J. The accuracy of needle placement in lower-limb muscles: a blinded study. Arch Phys Med Rehabil 2003;84:877-882.

27 28 Interventional Neuromuscular Ultrasound

John W. Norbury, MD Clinical Assistant Professor of Physical Medicine and Rehabilitation East Carolina University Director of the Musculoskeletal Ultrasound Laboratory Brody School of Medicine Greenville, North Carolina

Introduction can help them avoid perineural injections and allow the operator to choose the path between the skin and the target structure which The advent of high resolution ultrasound (US) presents clinicians is the safest, shortest, and easiest. US’s portability allows the with a powerful complement to the electrodiagnostic (EDX) procedure to be carried out efficiently in the office setting.5 In evaluation of conditions affecting the peripheral nervous system the author’s experience, US guidance also allows excellent local (PNS).1 The favorable cost profile of US compared with magnetic anesthesia so that that procedure is only mildly unpleasant or even resonance imaging may make it a valuable tool for obtaining painless for the patient. Finally, many patients enjoy “seeing” the anatomic information in patients with neuromuscular problems.2 pathology1 and sometimes even the real-time procedure image. Additionally, US gives the clinician a useful tool to treat many of Watching the images can even serve as a helpful distraction from the conditions seen in neuromuscular clinical practice. In theory, the procedure. a clinician can offer patients one-stop shopping with a diagnosis and treatment in the same visit.3 Interventional neuromuscular US Technical Aspects encompasses a range of procedures which are used to diagnose and treat conditions of the PNS using US guidance. Over 1,500 Interventional neuromuscular US presents the novice provider scientific publications support the use of US for these types of with a steep learning curve. This section of the review is devoted procedures.4 In practice most of these procedures consist of US- to clinical pearls which will help the beginner as they learn these guided regional anesthesia, US-guided biopsy of nerve lesions, procedures. and US-guided therapy with agents such as corticosteroids.5 This review will focus on the therapeutic applications of interventional US-guided procedures can be divided into direct and indirect neuromuscular US. For applications in regional anesthesia and guidance. Indirect guidance refers to marking the site of the target biopsy of soft tissue lesions the reader is directed to the reviews structure and then performing the intervention without real-time by Griffin4 and Kovacs,6 respectively. guidance. Direct guidance refers to the technique where the operator monitors the position of the needle in real time. Direct guidance There are several advantages to using US to guide procedures can further be divided into “in plane” or long axis approach and when compared with either blind procedures or other forms of “out of plane” or short axis approach (Fig. 1). Both have their guidance such as fluoroscopy, computed tomography (CT), and advantages and disadvantages. The long axis approach allows electrical stimulation. Unlike CT and fluoroscopic guidance, US- visualization of the needle during the entire procedure. The short guided interventions do not expose the patient or the provider axis approach is somewhat technically easier to perform and may to ionizing radiation. US-guided procedures are sometimes be desirable for some superficial structures. For neuromuscular perceived as less unpleasant than procedures guided by electrical procedures, the author prefers the long axis approach because stimulation. US also allows the operator to survey the area it allows direct visualization of the needle tip during the entire surrounding the target and identify structures which should be procedure for safer and more accurate needle placement. When avoided, such as vessels, tendons, and nerves. US interventions performing a long axis procedure, it is imperative to make the 29 Figure 2A Figure 1A Interventional Neuromuscular Ultrasound

Figure 1B A

Figure 2B B A

Figure 1. Comparison of the two approaches to direct ultrasound (US) guidance. The left side represents the probe and needle relationship and the right side represents the corresponding US image. (A) Example of the long axis approach. Note the “comet tail” artifact beneath the needle. (B) Example of the short axis approach. The needle appears as a hyperechoic dot and it may be difficult to determine the exact position of the needle bevel in space. angle between the needle and the transducer as parallel as possible. This will minimize anisotropy and improve visualization of the needle.

While there are many variations in the general approach to US- guided interventions, the following is the sequence of steps which the author employs in his laboratory. The most important B Figure 2C principle in performing any procedure is to keep in mind the Boy Scout Motto “Be Prepared.” In the author’s practice, an operator and an assistant are present during the procedure at all times. All equipment must be within reach of the operator prior to starting the procedure. Proper ergonomics is essential as repetitive stress injuries are very common among US practitioners7 (Fig. 2A). As vasovagal reactions happen from time to time, it generally is advisable to have the patient lie down during the procedure. It can be helpful to keep the needle out of the view of the patient.

Prior to performing a procedure, the operator should perform a diagnostic scan to identify the target structure. Doppler flow can assist in identifying blood vessels, nerves, and tendons which must be avoided. The skin can then be marked with an indelible pen (Fig. 2B). The area is prepped, draped, and an US transducer cover is applied. Vapocoolant spray is used for surface anesthesia prior to insertion of a small gauge (25 or 27) needle to inject local C anesthetic along a tract toward the target (Fig. 2C). This confers the advantage of excellent local anesthesia as well as a dry run Figure 2. Steps in the performance of an interventional neuromuscular of the procedure. Local anesthesia allows the operator to take ultrasound procedure to ensure proper ergonomics. This includes (A) their time while achieving optimal needle placement since the positioning the screen in front of the operator (which has the advantage of patient does not experience discomfort during this phase of the making it easy to look up and see the screen as soon as the needle has procedure. It is not advisable to spray vapocoolant directly on been inserted) and having a tray table with all supplies easily accessible, the probe as more than one US transducer has met its demise in (B) marking the area with an indelible pen (i.e., placing an X at the site of this fashion. Finally, a second needle is passed to administer the needle entry followed by a line at the side of the probe opposite the needle), therapeutic medication. In the case of corticosteroid preparations, and (C) applying vapocoolant spray with delivery of local anesthetic.

30 Figure 3A CAPTURING MOTION WITH ULTRASOUND: BLOOD, MUSCLE, NEEDLE, NERVE in tracking the needle (Fig. 3B). Finally, commercially available echogenic needles are sometimes easier to see than traditional needles.

Figure 3B Carpal Tunnel Injections A In the EDX laboratory, median neuropathy at the wrist is the most commonly encountered entrapment neuropathy in the upper limb. It is also the entrapment neuropathy most amenable to therapeutic intervention. A recent randomized controlled trial has demonstrated the short-term efficacy of blind carpal tunnel injections.8 A search of the Cochrane Database of Systemic Reviews has demonstrated improvement in symptoms for 1 month following a blind carpal tunnel injection; however, improvement beyond 1 month could not be demonstrated.9 In 2008, Smith described the ulnar approach for carpal tunnel injections which is the technique this author employs at his institution.10 In this technique, the median nerve is injected from the ulnar aspect of the tunnel, and the nerve is dissected from both the flexor tendons and the flexor retinaculum (Figs. 4 and 5). Evidence suggests that changes in gliding characteristics of the median nerve11 and changes in the subsynovial connective tissue12 are important factors in the development of carpal tunnel B syndrome (CTS). Presumably, these pathologies are addressed in an US-guided carpal tunnel injection, but not in a blind injection. Figure 3. Needle tracking techniques include: (A) beam steering—on In the author’s practice, a mixture of 1 cc 1% and 1 cc the left is the standard view of the needle and on the right is a view of 40 mg kenalog is used for this procedure. Prior to the injection, it the needle with beam steering (note how the needle is easier to visualize is important to inform patients that they will experience numbness on the right with a more prominent comet tail artifact) and (B) color flow for 1-2 hours. Patients who undergo a bilateral injection may be (shown here in black and white)—using Doppler will allow the needle tip advised to have an alternative driver available on the day of the to be visualized by the color signal (lighter colored area) created when the procedure. needle is jiggled back and forth. Other Injections the confirmation of successful placement will be made easier Several other entrapment neuropathies are amenable to diagnostic by the characteristic hyperechoic crystalline appearance of the and therapeutic US-guided injections. The technique for injecting injectate. Bear in mind that it is always important to keep the side the lateral femoral cutaneous nerve in patients with meralgia of the gloved hand or a finger in contact with the patient (with both paresthetica has been described by Hurdle.13 In this procedure, the needle hand and the transducer hand). This prevents slippage the anterior superior illiac spine (ASIS) is palpated, and the nerve during the procedure. is identified sonographicallyFigure just medial 4 to the structure. Due to

Needle tracking refers to the technique whereby the operator achieves continuous visualization of the needle during the entire procedure. Several principles are important to keep in mind in order to improve needle tracking or prevent or recover a “lost needle” during the procedure. After the site of entry has been marked with an indelible pen, it is important to meticulously line up the path of the needle with the long axis of the transducer. The needle is then inserted while the operator is viewing the probe and the needle on the skin. After the needle has been inserted at least as far as the transducer itself, then the operator shifts his or her gaze to the screen to confirm the needle placement. After this point, the Figure 4. Injection of the carpal tunnel based upon Smith’s ulnar approach. operator must either move the needle or the transducer, but not (A) Adhesions are believed to connect the median nerve to the flexor both at the same time. Often a “caffeine tremor” can be helpful retinaculum and the subsynovial connective tissue of the flexor tendons. whereby the needle is gently jiggled in the tissue. The resulting (B) The corticosteroid solution is injected deep to the median nerve to vibrations are used to localize the needle. Some commercially hydrodissect the median nerve from the flexor subsynovial tissue. (C) available US machines have software which can assist in needle The corticosteroid solution is injected between the flexor tendon and the tracking. One example of this is beam steering in which the angle median nerve resulting in the median nerve being completely bathed in of the beam is directed in a plane more perpendicular to the needle corticosteroid solution. to improve visualization (Fig. 3A). Color flow also can be useful 31 Figure 5A

Interventional Neuromuscular Ultrasound Similar procedures may be employed for conditions such as ulnar neuropathy at the elbow and entrapments of the posterior interosseus and anterior interosseus nerves. Figure 5B Summary A Interventional neuromuscular US is an emerging field which encompasses a range of procedures to treat pathology of the PNS. As with all of electrodiagnosis and neuromuscular US, practice, good technique, and experience are imperative to achieve mastery of this discipline. Median neuropathy at the wrist is a good example of a condition which can be treated by US-guided intervention. However, more research is needed to establish the superiority of B US guidance to blind injection in treatment of median neuropathy Figure 5. Ultrasonographic visualization of hydrodissection of the tissues at the wrist. The lateral femoral cutaneous nerve, painful stump surrounding the median nerve during injection with corticosteroid solution. neuromas, and possibly ulnar neuropathies at the elbow are (A) Pre- (left) and post- (right) dissection of the median nerve away from other potential targets. More aggressive interventions involving the subsynovial connective tissue. (B) Pre- (left) and post- (right) dissection fenestration of the entrapping structures may be on the horizon. of the median nerve from the flexor retinaculum. MN = median nerve, arrows = needle, arrowheads = corticosteroid solution References

1. Norbury JW, Cartwright MS, Walker FO, Gutierrez C, Moore DP, the variable course of the lateral femoral cutaneous nerve, US Mandel S. Ultrasonographic evaluation of entrapment neuropathies has clear advantages to blind techniques for injection. US also in the upper limb. Pract Neurol 2011;10:38-44. can be employed to treat painful stump neuromas with phenol 2. Parker L, Nazarian LN, Carrino JA, et al. Musculoskeletal imaging: preparations.14,15 Finally, recent data suggest that US has a role medicare use, costs, and potential for cost substitution. J Am Coll in mild ulnar neuropathy at the elbow.16 Presumably, the specific Radiol 2008;5:182-188. site and cause of entrapment would be an important factor in 3. Nazarian LN. The top 10 reasons musculoskeletal sonography is determining whether a corticosteroid injection would be helpful, an important complementary or alternative technique to MRI. AJR however this is an area where more research is needed. Am J Roentgenol 2008;190:1621-1626. 4. Griffin J, Nicholls B. Ultrasound in regional anaesthesia. Billing And Coding Anaesthesia 2010;65 Suppl 1:1-12. 5. Tagliafico A, Bodner G, Rosenberg I, et al. Peripheral nerves: At the time, the procedure code for US-guided interventions is ultrasound-guided interventional procedures. Semin Musculoskelet the 76882 modifier. It is recommended that images of the target Radiol 2010;14:559-566. structure and the needle at the target structure be stored in the 6. Kovacs P GH. Interventional techniques. In: Peer S BG, ed. High machine and/or the permanent medical record in order to bill for resolution sonography of peripheral nervous system. Berlin: the procedure. Springer-Verlag; 2008. pp 169-185. 7. Siegal DS, Levine D, Siewert B, et al. Repetitive stress symptoms Future Directions among radiology technologists: prevalence and major causative factors. J Am Coll Radiol 2010;7:956-960. While the advantages to US-guided interventions for the treatment 8. Peters-Veluthamaningal C, Winters JC, Groenier KH, Meyboom- of conditions such as CTS have been outlined above, concrete de Jong B. Randomised controlled trial of local corticosteroid scientific evidence establishing the benefits of these procedures injections for carpal tunnel syndrome in general practice. BMC is lacking at present. The benefits and cost-effectiveness of these Fam Pract 2010;11:54. interventions must be established in the literature in the near 9. Marshall S, Tardif G, Ashworth N. Local corticosteroid injection future to guarantee that third party payers will continue to support for carpal tunnel syndrome. Cochrane Database Syst Rev 2007;2. these procedures. 10. Smith J, Wisniewski SJ, Finnoff JT, Payne JM. Sonographically guided carpal tunnel injections: the ulnar approach. J Ultrasound Several experimental neuromuscular procedures are on the Med 2008;27:1485-1490. horizon. One exciting experimental interventional procedure is 11. Oh S, Belohlavek M, Zhao C, et al. Detection of differential gliding percutaneous “ligamentomy” of the transverse flexor retinaculum. characteristics of the flexor digitorum superficialis tendon and In this procedure, the median nerve is dissected away from the subsynovial connective tissue using color Doppler sonographic transverse carpal ligament with saline. Subsequently, the ligament imaging. J Ultrasound Med 2007;26:149-155. is repeatedly fenestrated with a needle similar to the technique 12. Ettema AM, Amadio PC, Zhao C, et al. Changes in the functional used for needle tenotomy of the common extensor tendon. If structure of the tenosynovium in idiopathic carpal tunnel successful, this intervention may provide an attractive alternative syndrome: a scanning electron microscope study. Plast Reconstr to surgical arthroscopic and open releases of the carpal tunnel. Surg 2006;118:1413-1422.

32 CAPTURING MOTION WITH ULTRASOUND: BLOOD, MUSCLE, NEEDLE, NERVE

13. Hurdle MF, Weingarten TN, Crisostomo RA, Psimos C, Smith 15. Gruber H, Glodny B, Kopf H, et al. Practical experience with J. Ultrasound-guided blockade of the lateral femoral cutaneous sonographically guided phenol instillation of stump neuroma: nerve: technical description and review of 10 cases. Arch Phys predictors of effects, success, and outcome. AJR Am J Roentgenol Med Rehabil 2007;88:1362-1364. 2008;190:1263-1269. 14. Gruber H, Kovacs P, Peer S, Frischhut B, Bodner G. Sonographically 16. Rampen AJ, Wirtz PW, Tavy DL. Ultrasound guided steroid guided phenol injection in painful stump neuroma. AJR Am J injection to treat mild ulnar neuropathy at the elbow. Muscle Nerve Roentgenol 2004;182:952-954. 2011;44:128-130.

33 34 Capturing Motion With Ultrasound: Blood, Muscle, Needle, and Nerve CME Questions 1. Performing which of the following adjustments on an 6. Nerve changes that occur at sites of chronic external pressure ultrasound instrument is most likely to reduce temporal do not include: resolution? A. Enlargement just proximal to the site of compression. A. Turning off the image average. B. Enlargement just distal to the site of compression. B. Adding more focal zones to the image. C. Proliferation of endoneurial fibroblasts and capillary endothelial C. Reducing persistence. cells followed by fibrosis. D. Increasing the transducer sensitivity. D. Enlargement at the site of compression. E. Shifting the time gain compensation levers. 7. A peripheral nerve transversely cut in an ultrasound 2. Which of the following techniques is most useful for examination does not show: measuring the mechanical duration of a fasciculation in A. More echogenicity than the surrounding muscles. muscle? B. Less echogenicity than the surrounding tendons. A. Needle EMG examination. C. Nerve fascicles as whiter tubular fascicles. B. Color flow Doppler imaging of muscle. D. An overall “honeycomb” appearance. C. Power Doppler imaging of muscle. D. Surface EMG electrodes. 8. In chronic nerve entrapment, nerve blood flow changes do E. M-mode ultrasound. not include: A. An increase in blood flow at the site of compression. 3. The audio output available from an ultrasound instrument B. A decrease in blood flow at the site of compression. represents which of the following? C. An increase in blood flow proximal to the site of compression. A. The frequency difference between insonated and reflected D. An increase in the number of blood vessels proximal to the site waves. of compression. B. A direct rendering of echoes from insonated tissue. C. A harmonic of the emitted sounds of contracting muscle. 9. Currently the most useful single test for diagnosis of a D. Echoes from moving particles in blood. chronic nerve entrapment is: E. Resonant frequency of microbubbles. A. Loss of mobility of the nerve. B. Excessive nerve mobility. 4. Which of the following techniques is most helpful for C. Alterations of nerve shape (e.g., flattening). detecting slow blood flow in tissues? D. Maximal cross-sectional area of the nerve just proximal to the A. Color flow Doppler imaging. site of entrapment. B. Power Doppler imaging. C. M-mode imaging. 10. Dynamic ultrasound of the median nerve at the wrist D. B-mode imaging. demonstrates which of the following findings? E. A-mode imaging. A. The median nerve has increased mobility in those with carpal tunnel syndrome (CTS) compared to controls. 5. Which statement relating to a peripheral nerve is incorrect? B. The median nerve has decreased mobility in those with CTS A. Nerves composed of a single fascicle are less vulnerable compared to controls. to ischemia from external pressure due to a superficially placed C. Median nerve mobility is the same in those with CTS and nutrient artery. controls. B. Fascicles are loosely bound by connective tissue and referred D. Median nerve mobility cannot be accurately assessed with to as the epineurium. ultrasound. C. Part of the function of the epineural connective tissue is to facilitate the dispersion of external compressive forces. D. Connective tissue within nerve fascicles is called endoneurium. 35 CME QUESTIONS 11. Which of the following muscle groups is most likely to enter 18. During which phase of the respiratory cycle do motor unit the carpal tunnel during extension of the fingers and wrist? potentials fire most actively in the diaphragm? A. Flexor digitorum superficialis. A. End expiration. B. Abductor pollicis brevis. B. Early to mid inspiration. C. Extensor digitorum communis. C. Mid expiration. D. Lumbricals. D. End inspiration. E. During expiration with the breath held. 12. If an individual has ulnar nerve dislocation during elbow flexion, which of the following is most likely to occur during 19. Advantages to ultrasound-guided neuromuscular ulnar motor nerve conduction studies if the standard distance interventions compared with fluoroscopy and computed measurement technique is used with the elbow flexed? tomography (CT) guidance include all of the following A. Calculation of nerve conduction velocity (NCV) across the EXCEPT: elbow will be accurate. A. Ability to survey soft tissues prior to the procedure. B. Calculation of NCV across the elbow will be falsely elevated. B. Less exposure to ionizing radiation. C. Calculation of NCV across the elbow will be falsely lowered. C. Avoidance of perineural injections. D. Calculation of NCV across the elbow will not be possible. D. Increased reimbursement for the provider.

13. Snapping triceps syndrome can lead to ulnar neuropathy at 20. Which of the following ultrasound-guided intervention the elbow when which of the following occurs? techniques allows visualization of the needle throughout the A. The triceps tendon snaps across the olecranon. entire procedure? B. The triceps tendon and ulnar nerve snap across the olecranon. A. Indirect long axis. C. The triceps tendon snaps across the medial epicondyle. B. Direct long axis. D. The triceps tendon and ulnar nerve snap across the medial C. Indirect short axis. epicondyle. D. Direct short axis.

14. Anatomic continuity of peripheral nerves can be 21. All of the following are suggested steps in the performance of demonstrated with all of the following neuromuscular a neuromuscular ultrasound guided intervention EXCEPT: ultrasound techniques EXCEPT: A. Having the patient lie supine to prevent vasovagal reactions. A. A cross-sectional view scanning over the entire length of the B. Keep the needle from the patient’s view if possible. suspected nerve lesion site. C. Perform a screening ultrasound examination prior to the B. A sagittal view scanning over the entire length of the suspected procedure. nerve lesion site. D. Spray the interface of the uncovered transducer and the skin C. Demonstration of nerve gliding in-plane, with visualization with vapocoolant. just distal and proximal to the suspected nerve lesion site. D. Increased Doppler signal just distal to the suspected nerve 22. Which of the following is NOT a recommended needle lesion site. tracking technique? A. Using color flow. 15. What is the safest approach to use for needle EMG of the B. Jiggling the needle. diaphragm? C. Moving the transducer and the needle at the same time. A. The lateral 4th intercostal space on the right. D. Using beam steering. B. The 6th intercostal space on the right. C. The medial 8th intercostal space on the left. 23. Which of the following is a component of the “ulnar D. Inferior to the xiphysternum. approach” to carpal tunnel injection as described by Smith? E. Inferior to the costal margin. A. A 4 cc mixture of 1% lidocaine and 40 mg/cc kenalog. B. Repeated fenestration of the transverse carpal ligament. 16. In what setting can ultrasound enhance the accuracy or C. Hydrodissection of the median nerve from the flexor tendon safety of needle EMG? subsynovium. A. When examining high risk muscles in anticoagulated patients. D. Intraneural injection of the median nerve. B. When examining severely denervated or atrophic muscles. C. During chemodenervation of spastic muscles. D. In obese patients or patients with altered anatomy. E. All of the above.

17. A white shadow coming in to the field of view during ultrasound examination of the diaphragm is most likely to be: A. The liver. B. The spleen. C. The lung. D. The stomach. E. A pneumothorax. 36 VISIT THE AANEM MARKETPLACE AT WWW.AANEM.ORG FOR NEW PRODUCTS

American Association of Neuromuscular & Electrodiagnostic Medicine 2621 Superior Dr NW Rochester, MN 55901 T: 507.288.0100 F: 507.288.1225 www.aanem.org