An anomalous accessory flexor digiti minimi profundus muscle: a case study.

A well-developed anomalous muscle within the forearm flexor compartment was discovered during a routine cadaveric dissection. The identified muscle originated from the intercompartmental septum on the medial side of the forearm just proximal to the wrist joint and inserted on the proximal phalanx of the fifth digit. When stressed, the tendon of the muscle produced flexion of the metacarpophalangeal joint of the fifth digit. Contiguous muscles, including the flexor digitorum profundus, displayed normal morphology. The muscle appeared to be an accessory belly of flexor digitorum profundus. The combination of an accessory flexor digitorum profundus muscle belly acting on the metacarpophalangeal joint of the little finger has not been previously reported. Based on its origin, insertion, and action we have named this variant accessory flexor digiti minimi profundus. This muscular variant could have clinical relevance, possibly affecting ulnar nerve function and circulation in the hand.