Morphometric studies of the muscular branch of the median nerve.

The branch from the median nerve to the thenar muscles has a proximal and lateral (recurrent) course and is vulnerable to lesions that affect these muscles. Because of its anatomical-clinical importance, this branch was studied in 60 palmar regions from 30 cadavers of adult individuals of both sexes, aged between 23 and 77 y. It arose from the lateral branch of the median nerve in 83.3% of the cases. Its origin was distal to the flexor retinaculum in 48.3%, at the distal margin of the retinaculum in 31.6%, in the carpal tunnel in 18.3% and proximal to the retinaculum in 1.7%; it pierced the retinaculum in 15%. The point of recurrence of the branch was localised topographically to 34.6 +/- 3.6 mm from the distal wrist crease; the angle between its recurrent course and the longitudinal axis of the hand averaged 66.8 degrees. In 50% of the cases the muscular branch innervated abductor pollicis brevis (APB), opponens pollicis (OP) and the superficial head of flexor pollicis brevis (FPB), in 40% it supplied only APB and OP, and in 10% a short muscular branch gave rise to independent branches in the palm and which supplied APB, OP and the superficial head of FPB. The so called "accessory thenar branch' was found in 38.3%.