Multiple nerve variations and third head of biceps brachii in upper limb – A case report

Sixty fresh cadaver upper extremities were dissected for a study of the course of the posterior interosseous nerve (PIN) in the radial tunnel, an area that varies but begins in the furrow between the brachioradialis and brachialis in the distal arm and ends at the distal edge of the supinator muscle in the proximal forearm. The radial nerve pierces the lateral intermuscular septum 13 cm above the elbow joint line. At 1.3 cm above the joint line the nerve divides into its posterior interosseous and superficial radial branches. The extensor carpi radialis brevis muscle received nerve supply from the superficial radial nerve, radial nerve, and PIN in 43%, 55%, and 2%, respectively. The PIN passed through the radial tunnel anterior to the radiohumeral joint and then coursed laterally and posteriorly beneath the arcade of Frohse, which is the proximal edge of the superficial layer of the supinator muscle. The arcade was tendinous in 57% of the cadavers and membranous in 43%. The distal edge of the supinator was tendinous in 65% of the specimens and membranous in 35%. The purpose of this article was to measure the various lengths of the PIN and to study possible compression sites at normal variations along the course of the PIN in the radial tunnel. No cases showed evidence of PIN compression in the radial tunnel.