Anomalous Flexor Digitorum Superficialis Muscle Belly Associated with Carpal Tunnel Syndrome.

Anomalous muscle bellies in the forearm generally are asymptomatic and appreciated in an academic sense during cadaveric dissections. Few prior anatomic variations in muscle bellies have been described with symptoms, and are associated even more rarely with carpal tunnel syndrome (CTS). We discuss the evaluation and management of a case of CTS associated with a muscle belly of the flexor digitorum superficialis to the index within the carpal tunnel.