Unusual variation of the extensor digitorum brevis manus: A case report.

An anomalous muscle, the extensor digitorum brevis manus (EDBM) was found at the dorsum of the right hand arising from the wrist capsule beneath the extensor retinaculum and inserting into the ulnar side of the basis of the proximal phalanx of the long finger. The EDBM was located superficial to the common extensor tendons of the fingers. We analyze the tendency of the dominant hand to be involved and the possible complications such as the appearance of the "fourth compartment syndrome" or attrition ruptures of the common extensor tendons. We report the various applications of the EDBM in surgery, such as its use as a flap in covering defects of the distal tibia. Finally, we present the different theories about the development of the EDBM and the treatment in symptomatic cases with division of the extensor retinaculum or complete surgical excision of the muscle.