Wrist denervation and the anterior interosseous nerve: anatomic considerations

Wrist denervation via resection of the distal anterior interosseous nerve (AIN) and the posterior interosseous nerve (PIN) is an effective treatment for chronic wrist pain. When performing this procedure through a dorsal approach we have been impressed by anatomic variations of the AIN. This has raised concerns about potential denervation of the pronator quadratus (PQ). The purpose of this study was to elucidate the anatomy of the AIN and PIN as encountered through a dorsal distal forearm incision.

Ten fresh-frozen cadavers were dissected. Before dissection radiographs were obtained to ensure accurate localization of the proximal ulnar head with a radiopaque marker. A dorsal approach to the distal forearm was made to identify the anatomy of the PIN and AIN. The location and diameter of all AIN branches were noted by using an operating stereoscopic microscope at x 25 magnification and a precision caliper. The PIN anatomy and size also were noted.

The anatomy of the AIN was variable. The average AIN diameter proximal to the PQ was 1.5 mm. The average number of AIN motor branches was 4.2. The largest PQ motor branch was the first motor branch and was located at an average distance of 37.9 mm from the proximal ulnar head. The last motor branch was found an average of 23.9 mm from the proximal ulnar head. In 9 of 10 specimens the sensory branch tunneled radially through the distal PQ and innervated the periosteum of the volar distal radius. In 4 of 10 specimens a separate branch to the distal radioulnar joint was present. We found an average PIN diameter of 0.87 mm.

Resection of the AIN at a point 4 cm proximal to the proximal point of the ulnar head would denervate completely the PQ in our cadaver population. Division of the AIN 2 cm proximal to the ulnar head would spare most of the PQ motor branches.