Anatomy of the extensor tendons to the index finger.

An anatomic study was performed to better delineate the extensor tendons of the index finger. Seventy-two cadaver hands were dissected. Classically, a single slip of the extensor digitorum communis (EDC) and a single slip of the extensor indicis proprius (EIP) are said to run to the index finger. The EIP is said to be ulnar to the EDC at the level of the metacarpal head. In dissections in this study, the classic description was noted in 58 of the hands. Ten hands had a double slip of the EIP. Two hands had a double slip of the EDC running to the index. Two hands had a single slip of the EIP either volar or radial to the EDC at the level of the metacarpal head. Thirteen hands (19%) showed anatomic variants of the EIP and EDC tendons at the level of the metacarpal head, differing from the classic description. Additionally, two hands showed aberrant tendons. A knowledge of these variants when performing tendon repair or EIP transfer is necessary.