The intra-muscular course and distribution of the anterior interosseous nerve within pronator quadratus: An anatomical study.

Background: The anterior interosseous nerve (AIN) is a terminal motor branch of the median nerve innervating the following three muscles from proximal to distal: Flexor pollicis longus (FPL), the radial half of flexor digitorum profundus (FDP), and the pronator quadratus (PQ). The aim of this study was to define the course of the AIN within the PQ to aid surgeons performing distal radial procedures. Methods: Ten embalmed cadaveric forearms were dissected to identify the path of the AIN within PQ. An en-bloc excision of the PQ with its supplying AIN and vasculature was performed to identify a safe zone where PQ can be elevated without damaging AIN. A scoping literature search was performed to identify other studies reporting the path of AIN through PQ. Results: The mean distance from the radial border of the radius perpendicular to the point at which the AIN enters the PQ was 22.3 mm (range 21-24 mm). The mean distance from the distal wrist crease to the AIN entering PQ was 74.3 mm (range 59-84 mm). The mean number of nerve branches to PQ was 5.2 (range 3-8). In all specimens, the AIN was found to lie on the radial side of the anterior interosseous artery (AIA). Conclusions: The AIN courses on the deep surface of the PQ in a longitudinal proximal to distal direction. A 'safe zone' was identified within 20 mm of the radial border of the distal radius, which may be utilised by surgeons in a muscle-splitting approach to the distal radius.