Bilateral Abductor Pollicis Longus Muscle Duplication

Abstract

The abductor pollicis longus (APL) muscle has been largely reported to be a subject of numerous variations affecting the origin, the number of bellies and tendons, and the patterns of tendons insertions. We report a bilateral APL muscle duplication as a variation encountered during dissections of the forearm and hand of an adult female cadaver. The APL muscle presented with two bellies and each belly had a distinct tendon. The main belly originated as usual from the posterior aspect of the lateral border of the ulna, the interosseous membrane and the middle third of the radius while the additional belly was arising from a retinaculum‐like fascia formation attached at the lateral border of the radius and covering the extensor carpi radialis longus and brevis and both tendons inserted as usual on the base of the first metacarpal bone. The tendon from the additional belly was the most laterally inserted and therefore thought to be the main abductor, whereas the tendon from the main belly was thought to be the best extensor of the trapezo‐metacarpal joint. The presence of additional APL tendons has been regarded as a determinant in the development of De Quervain's stenosing tendovaginitis and the awareness of the existence of such anatomical variations may be important for reconstructive surgery as a potential source of transplant material.