Anomalous Extensor Indicis Proprius Muscle Extending Beyond the Extensor Retinaculum: A Case Report.

EIP is commonly used as a tendon transfer for extensor pollicis longus rupture. Few anatomic variants of EIP have been reported in the literature, but such variants should be considered because of their consequences to the success of tendon transfer and potential implications for diagnosis of an otherwise unexplained mass of the wrist.