The Pronator Quadratus and Distal Anterior Interosseous Nerve: A Cadaveric Study

Background The pronator quadratus (PQ) muscle is an important and commonly encountered structure in surgery of the wrist. A thorough understanding of the anatomy of the PQ and the anterior interosseous nerve (AIN), which innervates the PQ, is important, particularly during distal radius fracture osteosynthesis and distal AIN transfer to deep branch of the ulnar nerve. Furthermore, there is a paucity of literature regarding sex differences in the morphology of these structures. We describe the morphology of the PQ and AIN and compare PQ and AIN findings in male and female specimens. Methods Twenty-five cadaveric upper extremities underwent loupe-aided dissection of the volar forearm with identification of the AIN and PQ. A digital photograph taken perpendicular to the volar surface of the forearm was used tomeasure the PQ and assess AIN morphology using ImageJ (National Institutes of Health; Bethesda, MD). Comparisons between male and female specimens were performed. Results Of the 25 specimens, 84% appeared as a single trapezoidal muscle bundle, with the remaining 16% demonstrating a double-bundle morphology. The PQ was a mean 3.8 +/- 0.5 cm in radial-ulnar width and 4.6 +/- 0.7 cm in proximal-distal length with a mean thickness, area, and volume of 0.6 +/- 0.2 cm, 18.2 +/- 4.8 cm(2), and 10.5 +/- 3.7 cm(3), respectively. The PQ branch of the AIN was a mean 3.8 +/- 1.1 cm long and had a mean diameter of 1.4 +/- 0.2 mm. Male specimens demonstrated significantly greater radial-ulnar width (p = 0.005), area (p = 0.006), and volume (p = 0.033) of the PQ, as well as a greater distance from the radial styloid to the distal arborization of the AIN (p = 0.005) compared with female specimens. Conclusions The current study informs hand surgeons of the morphologic variability and sexual dimorphism of the PQ and AIN and may help guide operative planning.