Variations in innervation of the flexor digitorum profundus muscle

The composite flexor digitorum profundus muscle has a dual nerve supply fro m the ulnar nerve (UN) and the anterior interosseous nerve (AIN) but anatom ic data regarding the territories of these 2 nerves are limited. In this st udy, muscles from 20 cadaver forearms were dissected microscopically. The m otor nerves were followed to their terminations on individual muscle bellie s and the innervation domains mapped. In 75% of cases the AIN supplied the index and middle fingers and the UN supplied the middle, ring, and little f ingers; thus, the middle finger had dual innervation. In 20% of cases the A IN went to the index and middle fingers and the UN went to the ring and lit tle fingers. In 5% of cases the AIN went to the index finger and the UN wen t to the middle, ring, and little fingers. The motor entry points were norm alized to the forearm length. The entry points of the UN and AIN branches w ere at 15%. and 30% of forearm length, respectively, distal to the medial e picondyle. (J Hand Surg 1999;24A:700-703. Copyright (C) 1999 by the America n Society for Surgery of the Hand.).