Flexor digitorum accessorius longus.

A supernumerary muscle in the ankle joint, the flexor digitorum accessorius longus, was found in 12 of 100 cadavers (12%). The muscle originated either by 2 heads (a long and a short one) or by a single head, from any of the deep structures of the posterior compartment of the leg. It descended in the tarsal tunnel, superficially and close to the neurovascular bundle and to the tendon of the Flexor hallucis longus muscle, to insert into the tendon of the Flexor digitorus longus in the planta. During this course, the muscle very frequently preserved its fleshy fibers, and could easily be identified by this characteristic. The possibility of such a muscle being a factor of compression in a "tarsal tunnel syndrome" should be kept in mind.