Median Nerve

Anatomy

Branches medial and lateral cords. (C5-T1)

 

Motor

Supplies all flexor muscles EXCEPT flexor carpi ulnaris and and medial half of flexor digitorum profundus (supplied by ulnar nerve)

  • Pronator teres

  • Flexor carpi radialis

  • Flexor digitorum superficialis

  • Palmaris longus

  • Abductor pollicis brevis (APB best thenar muscle to test function of median nerve in the hand)

  • Flexor pollicis brevis (Note FPB and OP get dual innervation with ulnar nerve)

  • Opponens pollicis

  • Lateral two lumbricals

Via anterior interosseous branch (branch of median nerve at level of pronator teres)

  • Flexor pollicus longus

  • Pronator quadratus

  • Flexor digitorum profundus to the index and middle finger

Sensory

Palmar cutaneous branch (branches proximal to carpal tunnel) - provides sensation to thenar skin of the palm

After carpal tunnel - Terminal branches supply the thumb, index, long and radial half of ring finger (radial 3 1/2  fingers)

 

Course

Runs within the lateral intermuscular septum, deep to the short head of the biceps and lateral to the brachial artery. It crosses to the medial side of the brachial artery mid upper arm and descends to the antecubital fossa. No branches in upper arm or axilla.

In the antecubital fossa, the median nerve lies deep to the bicipital aponeurosis, medial to the antecubital vein, and medial to the brachial artery. Lies superficial to brachialis and passes through the two heads of Pronator teres. It then descends deep to deep to the flexor digitorum superficialis and superficial to the flexor digitorum profundus. In the distal 1/3 of the forearm, the median nerve emerges from beneath the flexor digitorum superficialis to lie medial to the flexor carpi radialis and lateral to the palmaris longus before entering the carpal tunnel.

 

Branches

Anterior interosseous nerve

  • Distal part of antecubital fossa, passes inferiorly on the interosseous membrane with anterior interosseous branch of Ulnar artery, It runs between flexor digitorum profundus and flexor policis longus to reach  pronator quadratus. Ends in sensory fibres to wrist joint 

Palmar cutaneous branch

  • Arises about 4 to 5 cm proximal to the wrist and passes SUPERFICIAL to the flexor retinaculum to supply the skin over the thenar eminence.

Recurrent motor branch

  • Motor to thenar muscles, course is variable may emerge distal to flexor retinaculum or pierce flexor retinaculum mid substance.

Clinical

 

Sites of entrapment

  • Proximal - The median nerve may be compressed by 4 different structures at the elbow: The proximal ligamentous attachment of the humeral head of the pronator teres (ligament of Struthers), lacertus  fibrosis, muscle belly of the pronator, or the proximal edge of the flexor digitorum superficialis.

  • Distal - Carpal tunnel syndrome. Symptoms of carpal tunnel syndrome manifest as numbness and dysaesthesias in the radial three and one half digits of the hand and in the most severe cases it progresses to weakness in the thenar musculature.

References

Mazurek, Michael T. MD. Shin, Alexander Y. MD. Upper Extremity Peripheral Nerve Anatomy: Current Concepts and Applications. Clinical Orthopaedics & Related Research. 1(383):7-20, February 2001.

Ristic, Sasha MD. Strauch, Robert J. MD. Rosenwasser, Melvin P. MD. The Assessment and Treatment of Nerve Dysfunction After Trauma Around the Elbow. Clinical Orthopaedics & Related Research. (370):138-153, January 2000.

Last updated 11/09/2015