(aspects of sports medicine • a case report) Peroneal Nerve Compression Secondary to an Anomalous Biceps Femoris Muscle in an Adolescent Athlete Kevin M. Kaplan, MD, Abhay Patel, MD, and Drew A. Stein, MD ABSTRACT compression can present a consid- 3/5, with all other muscle groups Common peroneal nerve compres- erable challenge. Other conditions 5/5. Sensation was significantly sion is a well-recognized entity must be excluded in order to make decreased at the first dorsal web that can cause severe debilitating the proper diagnosis.3 Symptoms space and the dorsal lateral foot. clinical manifestations. The cur- can occur after exercise, can develop Pulses were intact, and all reflexes rent literature describes numerous gradually after a period of training, were 2+ with negative clonus and locations and mechanisms of com- pression, including both structural or can have an insidious onset. Babinski reflexes bilaterally. The and systemic causes. Anatomical We present the case of a 14-year- patient had no lumbar tenderness variants should be considered old basketball player who developed and had a negative straight leg part of the differential diagnosis a compressive neuropathy of the raise bilaterally. in peroneal nerve impingement. common peroneal nerve secondary to On the basis of the clinical his- We present the case of a 14-year-old an accessory biceps femoris muscle. tory and physical examination, the basketball player with footdrop sec- ondary to compression of the com- mon peroneal nerve from an acces- sory biceps femoris muscle, which “...the diagnosis of an accessory biceps was treated by neurolysis. In addition, we review the systematic workup of femoris muscle should be part of the patients with nerve compression. differential diagnosis for footdrop.” he common pero- neal nerve is a periph- CASE REPORT patient was diagnosed with right eral nerve in the lower A 14-year-old basketball player pre- lower extremity footdrop with weak- extremity susceptible to sented with an 8-month history of ness and decreased sensation in the Tentrapment secondary to its tortuous increasing right foot weakness and distribution of the common pero- path and relationship to the fibular numbness associated with dull leg pain. neal nerve. X-rays of the knee and head.1,2 Determining the etiology Over the course of several months, lumbar spine were negative. Lumbar and exact anatomical site of nerve symptoms progressed, precluded him spine magnetic resonance imaging from participating in athletics, and (MRI), performed to exclude spine Dr. Kaplan is Orthopaedic Resident, eventually led to difficulty ambulating. pathology, showed no spinal stenosis, Hospital for Joint Diseases, New York, The majority of numbness was local- nerve root impingement, or intra- New York. Dr. Patel is Orthopaedic Resident, ized to the dorsum of the foot, and the spinal pathology. Electromyography Maimonides Medical Center, Brooklyn, patient was unable to actively dorsiflex (EMG) and a nerve conduction study New York. the ankle. He denied any history of subsequently indicated severe right Dr. Stein is Orthopaedic Surgeon, Sports trauma and medical problems and any common peroneal nerve dysfunction. Medicine, Hospital for Joint Diseases, recent weight loss, fevers, rashes, other No response was elicited 0.5 cm New York, New York, and Maimonides Medical Center, Brooklyn, New York. illnesses, back pain, and bladder and proximal to the fibular head; how- bowel disturbances. ever, there were normal distal latency, Address correspondence to: Drew Stein, On physical examination, the conduction velocity, and only mildly MD, 301 East 17th Street New York, NY patient ambulated with a right lower diminished amplitude below the level 10003 (tel, 212-598-6000; fax, 212-398- extremity steppage gait. Ankle of the fibular head. 8356; e-mail, [email protected]) dorsiflexion and extensor hallucis Right knee MRI, used to evaluate Am J Orthop. 2008;37(5):268-271. longus strengths were 2/5, and he for etiologies of common peroneal Copyright Quadrant HealthCom Inc. 2008. was unable to stand on the right nerve compression, showed that the All rights reserved. heel. Ankle eversion strength was biceps femoris muscle was prominent 268 The American Journal of Orthopedics® K. M. Kaplan et al Biceps femoris m. Biceps femoris tendon Accessory biceps femoris m. common peroneal n. A C E Gastrocnemius m. the accessory biceps femoris muscle (Figure 6). Neurolysis of the com- Biceps femoris m. mon peroneal nerve was performed at the level of the biceps femoris and Biceps then distal to the fibular tunnel after femoris the nerve bifurcation (Figure 7). The tendon nerve was judged to be free of any compression throughout a range of motion of the knee. After surgery, the common peroneal n. patient began a physical therapy regi- D B Gastrocnemius m. men emphasizing tibialis anterior and peroneus longus strengthening. Figure 1. Axial magnetic resonance imaging shows a prominent biceps femo- During the first 2 weeks after ris muscle: (A,B) Large white arrow points to an anomalous accessory biceps surgery, the patient’s symptoms femoris posterior to the tendon. As the biceps femoris normally approaches the improved significantly. By 2 months level of the fibula, no muscle should be located posteriorly to the tendon. (C) after surgery, the patient had regained More distal cut on which the nerve should appear traversing anterior to the fibula full ankle dorsiflexion and ankle ever- but remains posterior secondary to the accessory muscle. Legend for Parts sion strength compared with the con- A-C: small white arrow points to compression of the common peroneal nerve; tralateral side. He was able to stand arrowhead indicates the true biceps muscle (white circle indicates the biceps on his heel and perform a single-leg tendon); and asterisk marks the lateral head of the gastrocnemius. (D,E) Normal stand without any difficulty. He also cross-section and cross-section with an accessory biceps femoris, respectively. displayed a normal heel–toe gait pat- Illustrations by NYU Hospital for Joint Diseases Graphics Department. tern. Furthermore, the paresthesias and complaints of leg pain resolved. close to its fibular insertion and con- surgery, the patient was placed in a A second EMG nerve conduction tained an accessory muscle (Figure custom-made ankle-foot orthosis. study showed substantial improve- 1). The peroneal tendons demon- In the operating room, the patient ment in nerve conduction and only strated increased uptake secondary received general anesthesia and minimal neurogenic dysfunction of to edema, which is the result of was placed in the lateral decubitus the common peroneal nerve at the nerve compression (Figure 2). The position. Under tourniquet, a 6-cm level of the fibular head. The distal signal intensity, which may be related incision was made over the fibu- latency and amplitude returned to to loss of vasomotion and vascular lar head along the course of the normal, and only a mildly delayed responses to vasoactive substances, biceps femoris muscle (Figure 3). A conduction velocity across the fibular occurred secondary to muscle dener- blunt dissection technique was used head was observed. With the signifi- vation. The common peroneal nerve to identify and then incise the fascia cant improvement in the EMG nerve was compressed because of its anom- of the biceps femoris, after which the conduction studies and an essentially alous course around the accessory common peroneal nerve was identi- normal neurologic examination, the biceps femoris and was not allowed fied (Figure 4). Subsequently, the patient was allowed to discontin- to assume its normal anatomical posi- accessory biceps femoris muscle was ue physical therapy and return to tion in relation to the fibula until identified close to its distal inser- sports as tolerated. At 1-year follow- distally in the leg (Figure 1). On the tion at the fibular head (Figure 5). up, the patient had no complaints basis of MRI and clinical findings, The common peroneal nerve was and a normal physical examination common peroneal nerve release and followed distally until its bifurcation and had returned to previous levels of neurolysis were indicated. Before and was noted to be compressed by athletic activity. May 2008 269 Peroneal Nerve Compression Figure 2. Axial magnetic resonance Figure 4. Incision with underlying Figure 6. Release of compression imaging shows increased uptake in the fascia and identification of common at site of accessory biceps femoris peroneal muscles consistent with com- peroneal nerve. muscle. pression of the common peroneal nerve. Figure 3. Marking of incision. Figure 5. Identification of acces- Figure 7. Visualization of bifurcation sory biceps femoris muscle at end of the common peroneal nerve. of forceps. DISCUSSION weakness, and paresthesias. Stage III compartment syndrome must also be The common peroneal nerve origi- presents with constant pain, evidence in the differential diagnosis, noting nates as a branch of the sciatic nerve of muscular atrophy, and irreversible that neurologic changes from a com- and has contributions from nerve sensory loss. partment syndrome are typically late roots L4 to S2. As it travels down Compression or entrapment can in the clinical course. the thigh, the nerve supplies the short occur in various locations, but certain Several causes of common perone- head of the biceps femoris along its anatomical sites are commonly asso- al compression have been described medial side and then crosses, pos- ciated