Supernumerary extensor tendon to the thumb: a case report.

Anomalies of the dorsal tendons of the hand are not uncommon. Numerous variations in the tendons coursing through the fourth dorsal extensor compartment have been described. We report a rare case of a supernumerary tendon passing through the fourth dorsal compartment and inserting into the distal phalanx of the thumb. We also review the anomalous muscles and tendons that are found in this compartment.