Uncommon Nerve Compression Syndromes of the Upper Extremity John D. Lubahn, MD, and Mary Beth Cermak, MD Abstract Nerve compression syndromes are a common cause of pain, sensory distur- eighth roots of the brachial plexus. bance, and motor weakness in both the upper and the lower extremities. These fibers course through the Although carpal tunnel syndrome is frequently diagnosed and treated surgical- posterior divisions of the upper, ly with success, other compression syndromes are less common and are often middle, and lower trunks, forming best treated nonsurgically. Understanding the anatomy of the major peripheral the posterior cord and, subse- nerves with respect to intermuscular septa, fibrous bands, muscle margins, and quently, the radial nerve arising internervous planes is crucial to understanding how and where peripheral from the posterior cord. The nerve compression can occur. Some conditions, such as anterior interosseous nerve passes anterior to the sub- nerve syndrome, respond well to nonoperative treatment; others, such as poste- scapularis, teres major, and latis- rior interosseous nerve syndrome, are better treated by surgical intervention. simus dorsi muscles, where the The authors discuss the anatomic and pathologic causes for compression syn- first potential site of compression dromes, as well as guidelines for treatment and outcomes. may occur. Although rare, an J Am Acad Orthop Surg 1998;6:378-386 anomalous muscle, the accessory subscapularis-teres-latissimus, has been reported to cause compres- sion of the radial nerve at this Compression syndromes of periph- nerve may be interpreted as a level.6 Spinner7 has described eral nerves have a number of possi- painful stimulus by the brain. To penetration of the nerve directly ble causes. Pressure on a nerve may describe the extent of compression by the subscapular artery more disrupt either the local blood flow or and/or injury to a nerve, classifica- distally in the axilla, forming a the axoplasmic flow to the nerve. tion systems have been developed neural loop and potentially result- Low blood pressure may diminish by Sunderland4 (Table 1) and by ing in compression. Exiting the the blood supply of peripheral Seddon5 (Table 2). Peripheral axilla, the radial nerve courses lat- nerves and cause the familiar dys- nerve dysfunction secondary to erally, passing through the trian- esthesias, paresthesias, and occa- viral illness or exposure to toxins, gular space and then proceeding sional motor weakness about which such as heavy metals, can mimic through the lateral head of the tri- patients frequently complain. Direct compression syndrome. Patients ceps, where Lotem et al8 and other pressure of 500 mm Hg or more with systemic diseases, such as dia- may cause internal disruption of the betes, may be more susceptible to axons.1 Epineurial scarring may nerve compression. Lifestyle and spontaneously form in peripheral behavioral patterns may also influ- Dr. Lubahn is Chairman, Department of nerves, with resultant symptoms of ence the occurrence of nerve com- Orthopaedic Surgery, Hamot Medical Center, partial or complete compression pression, as in the ÒSaturday night Erie, Pa. Dr. Cermak is Instructor and (Fig. 1).2,3 palsyÓ seen in alcoholics. Orthopaedic Surgeon, Hamot Medical Center. Motor nerves, such as the poste- rior interosseous branch of the Reprint requests: Dr. Lubahn, Hand, Micro- surgery and Reconstructive Orthopaedics, 300 radial nerve and the anterior Radial Tunnel Syndrome State Street, Suite 205, Erie, PA 16507. interosseous branch of the median nerve, contain stretch receptors, Pathoanatomy Copyright 1998 by the American Academy of sensory fibers, and motor fibers. The radial nerve is composed of Orthopaedic Surgeons. Therefore, pressure on a motor fibers from the sixth, seventh, and 378 Journal of the American Academy of Orthopaedic Surgeons John D. Lubahn, MD, and Mary Beth Cermak, MD and the flexor carpi radialis in the distal third of the forearm to lie superficial and subcutaneous. The deep branch of the radial nerve (the posterior interosseous branch) passes through the so- called radial tunnel, where it once again becomes subject to compres- sion. The radial tunnel is composed of the anatomic structures between the radiohumeral joint and the dis- tal extent of the supinator muscle. Potential sites of compression causing radial tunnel syndrome include the fibrous margin of the extensor carpi radialis brevis mus- cle, fibrous bands at the level of the radiocapitellar joint, the radial Fig. 1 Compressive lesion in the radial nerve. The constriction was intraepineurial, and recurrent artery, the arcade of the patient was treated with epineurolysis. Recovery was slow, and tendon transfers were Frohse proximally as the nerve performed. The lesion resolved over the course of 5 years, with electromyographic evi- passes distally through the supina- dence of return of normal function. (Courtesy of Graham D. Lister, MD, Vero Beach, Fla.) tor muscle, and a fibrous band at the distal margin of the supinator muscle.11,12 Once through the researchers have reported com- and a deep branch. The superfi- supinator, the deep branch of the pression. (Lotem et al correlated cial branch contains sensory fibers radial nerve divides into superfi- the data obtained in cadaveric and continues beneath the bra- cial and deep components. The studies with findings from clinical chioradialis into the forearm, pass- superficial branch courses medial- studies. Surgery was not per- ing between the brachioradialis ly, innervating the extensor digito- formed to verify the exact cause of the compression.) Familial radial nerve entrapment Table 1 has been reported secondary to SunderlandÕs Classification of Nerve Compression4 compression at the lateral head of the triceps.9 A genetic defect in Grade Description Schwann cell myelin metabolism has also been postulated as a cause 1 Interruption of axial conduction at the site of injury. The axon of radial tunnel syndrome.10 Al- remains in continuity; some segmental demyelinization may be though this disorder may be present but not Wallerian degeneration. The condition is reversible. asymptomatic, it can predispose the nerve to intermittent compres- 2 The axon itself is no longer in continuity. The axon does not sion. survive distal to the level of the injury and for a short distance The nerve then courses distally proximal. The endoneurium is preserved. Full recovery may be along the humerus and passes expected. from the posterior to the anterior 3 The axon is severed, and Wallerian degeneration develops. The compartment of the arm, where endoneurial tube is lost, and the fascicular anatomy is disturbed. yet another potential site of com- Recovery is incomplete. pression, the lateral intermuscular 4 Total destruction of the internal architecture of the nerve. The septum, is found. Following the trunk is intact, but a neuroma will form. Spontaneous recovery deep surface of the brachioradialis is rare. Surgical repair is indicated. and the extensor carpi radialis longus muscles, the radial nerve 5 Loss of continuity of the nerve trunk. Surgical repair is mandatory. bifurcates into a superficial branch Vol 6, No 6, November/December 1998 379 Nerve Compression in the Upper Extremity well established. Treatment may Table 2 include rest, stretching exercise, 5 SeddonÕs Classification of Nerve Compression and splinting.14,15 If symptoms have not improved after 6 to 12 Type Definition weeks, a corticosteroid injection carefully placed adjacent to, but Neurapraxia Pressure on the nerve with resultant dysesthesias but no loss not within, the nerve is an accept- of continuity able therapeutic option.14,15 Axonotmesis The neural tube is intact, but the internal axons have been Surgical intervention may be disrupted considered if the symptoms are not Neurotmesis The nerve itself has been completely divided relieved by rest, activity modifica- tion, nonsteroidal medication, or a cortisone injection. Before consid- ering surgical treatment, precise rum, the extensor digiti minimi, extension and forearm supination localization of the pain to the and the extensor carpi ulnaris against resistance may also repro- region directly over the radial muscles. The deep branch contin- duce the pain.11 However, this nerve within the radial tunnel must ues distally to supply the abductor maneuver (among others) will also be confirmed. Lister et al11 have pollicis longus, the extensor polli- cause pain with lateral epicondyli- recommended decompression of cis brevis, the extensor indicis pro- tis. Forearm pain may be produced the radial nerve through a trans- prius, and the extensor pollicis by resisted supination with the verse incision at the level of the longus. elbow extended or by resisted supinator when the surgeon is extension of the middle-finger absolutely certain that the site of Clinical History and Symptoms metacarpophalangeal joint with the compression is the supinator. If Pain is the most common prima- elbow extended and the forearm doubt exists because of tenderness ry presenting symptom in radial supinated. These maneuvers pur- proximally over the radial nerve, a tunnel syndrome. There is some portedly produce compression of more extensile, bayonet-shaped controversy concerning the exis- the nerve by the fibrous arch of the incision beginning at the level of tence of this syndrome because it is supinator and extensor carpi radi- the lateral epicondyle and extend- based essentially on the presence alis brevis muscles, respectively. ing in