A Gantzer muscle arising from the brachialis and flexor digitorum superficialis: embryological considerations and implications for median nerve entrapment.

Gantzer muscles are variant muscles in the anterior forearm inserting into the flexor pollicis longus or, less often, the flexor digitorum profundus. The presence of Gantzer muscles can cause a compressive neuropathy affecting the anterior interosseous nerve (Kiloh-Nevin syndrome). These muscles must also be considered when anterior forearm fasciotomies are performed for the management of acute compartment syndrome. In this case report, a novel Gantzer muscle originated from the flexor digitorum superficialis as well as the investing fascia of the brachialis muscle; the latter site is a novel proximal attachment not previously reported. In addition, the Gantzer muscle possessed rare characteristics because it (1) possessed a split tendinous distal insertion into both the flexor pollicis longus and flexor digitorum profundus, (2) exhibited a triangular morphology, and (3) was innervated by the median nerve. Most importantly, the dual origin of this Gantzer muscle formed a tunnel containing branches of the median nerve; therefore, this report documents a unique anatomical scenario in which the Gantzer muscle may compress and cause entrapment of aspects of the median nerve.