Gantzer's muscle. An anatomical study of the accessory head of the flexor pollicis longus muscle.

The relationship of Gantzer's muscle (the accessory head of flexor pollicis longus; FPL) to the median nerve and its anterior interosseous branch is debated. In an anatomical study of 25 limbs, the incidence, origin, insertion, nerve supply and relations of Gantzer's muscle have been documented. The muscle was found in 13 of the 25 (52%) limbs and was supplied by the anterior interosseous nerve. It arose from the medial humeral epicondyle in 85% and had a dual origin from the epicondyle and coronoid process in the rest. Its insertion was to the ulnar part of FPL and its tendon. Gantzer's muscle always lay posterior to both the median and anterior interosseous nerves. Anatomical variations in which Gantzer's muscle may contribute to median nerve compression in pronator syndrome are discussed.