Extensor Digitorum Brevis Manus, a Differential Diagnosis

Abstract

The extensor digitorum brevis manus muscle is a variant of the hand extensors. It is a supernumerary muscle on the dorsum of the wrist, located in the fourth extensor compartment. It is usually asymptomatic, but when it causes discomfort, it manifests as a painful mass. When it is symptomatic, surgical treatment is recommended, which may include muscle excision or extensor retinaculum release. We present a 30-year-old patient with a painful mass on the dorsum of the left hand; clinically, a ganglion was suspected and scheduled for surgical resection. She underwent surgery and was diagnosed with symptomatic EDBM, which was treated with extensor retinaculum release. EDBM was found incidentally in a cadaveric dissection; therefore, its true incidence is unknown. EDBM originates in the wrist joint capsule, below the dorsal radiocarpal ligament; its distal insertion is the ulnar side of the extensor mechanism in the metacarpophalangeal joint where it is present. Innervated by the posterior interosseous, research has shownthat its purpose is to extend and deviate the finger towards the side where it is inserted. This case is particularly interesting given the scarcity of information on its incidence and prevalence, with the majority of that information coming from postmortem reports.