Median nerve anatomy and entrapment syndromes: a review

Clinicians commonly observe upper extremity signs and symptoms which result from median nerve entrapment and can develop at multiple sites along this nerve. Median nerve entrapment may occur at the distal humerus when the rarely present ligament of Struthers connects an anomalous bony spur of the humeral shaft to its medial epicondyle. The pronator syndrome refers to compromise of the median nerve in the proximal forearm region. This may result from entrapment between the 2 heads of the pronator teres, between the pronator teres and the flexor digitorum sublimis, or by the lacertus fibrosus extension from the biceps tendon. The anterior interosseous branch of the median nerve is subject to compromise near its origin. As a motor nerve it produces signs of weakness as indicators of anterior interosseous syndrome. This syndrome usually occurs spontaneously, but can be caused by fractures and fibrous bands. The carpal tunnel is a narrow fibro-osseous tunnel through which the median nerve passes with 9 tendons. Carpal tunnel syndrome is the most common of the median nerve entrapments. Its causes are many: anything which increases the volume of the tunnel contents or decreases the size of the tunnel. Electrodiagnostic abnormalities exist more frequently when this entrapment is present than for other median nerve entrapments. Anatomic variations of the median nerve occur frequently and may lead to diagnostic confusion if not recognized. Successful diagnosis and treatment of median nerve entrapment syndromes require awareness of possible involved sites and detailed knowledge of related anatomy.