Median nerve lesions
The median nerve arises from the brachial plexus and supplies the flexor aspect of the forearm and the following short muscles of the hand (LOAF) – the Lateral two lumbricals,Opponens pollicis, Abductor pollicis brevis and Flexor pollicis brevis).
Median nerve injuries tend to occur near the wrist or high up the forearm. Where the median nerve passes through the anterior cubital fossa under the biceps aponeurosis into the forearm it is vulnerable to damage by forearm fractures and elbow dislocations (high lesions). It then passes under the flexor retinaculum (through the carpal tunnel) into the hand – low lesions are caused by compression in carpal tunnel syndrome (see below), cuts to the wrist or carpal dislocation.
Low lesions: There is loss of muscle bulk in the thenar eminence, abduction and opposition of the thumb are weak and sensation is lost over the radial three and a half digits on the palmar surface.
High lesions: In addition to the clinical findings of a low lesion, the long flexors of the thumb, index and middle fingers are paralysed.
If the nerve is severed suture or grafting should be attempted.