Anatomy of the thenar branch of the median nerve.

The gross and interfascicular anatomy of the terminal portion of the thenar (or recurrent median) nerve was defined by a microdissection of 20 fresh-frozen cadaveric hands. The traditionally described pattern of one main thenar trunk with three terminal branches, one each to the abductor pollicis brevis, opponens pollicis, and flexor pollicis brevis muscles, was observed in nine specimens (45%). One main trunk with two terminal branches (one branch to the abductor and one to the opponens, but no branch to the flexor) was seen in six specimens (30%). The remaining five specimens (25%) exhibited four other terminal patterns with either two, three, or four branches off the main trunk. In 15 specimens (75%), a previously undescribed "accessory thenar nerve" (ATN) arose from either the first common digital nerve (25%) or the radial proper digital nerve to the thumb (50%). The ATN innervated the flexor pollicis brevis.