An accessory muscle of flexor digitorum profundus with bipennate first lumbrical: a unique variation of clinical significance

During the deep dissection of the front of the forearm, an anomalous accessory muscle in relation to the flexor digitorum profundus (FDP) muscle was observed in the right forearm. The accessory muscle consisted of a spindle-shaped muscle belly with a long tendon underneath the flexor pollicis longus muscle. When followed distally, the accessory muscle tendon was found lateral to the FDP tendon for the index finger and entered the palm deep to the flexor retinaculum. In the palm, we encountered the first lumbrical muscle as a bipennate muscle taking origin from the adjacent sides of the middle of the tendons of FDP and accessory muscle tendon. After giving origin to first lumbrical muscle, the accessory muscle got merged with the tendon of FDP for index finger. Understanding this kind of variation is required for radiologists and hand surgeons for diagnostic purposes and while performing corrective surgical procedures.