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.