Anatomic Landmarks for the Radial Tunnel

Background: The posterior interosseous nerve (PIN) can be difficult to locate within the radial tunnel. The deep branch of the radial nerve (DBRN) enters the supinator muscle after passing under the arcade of Fröhse. It courses through the superficial portion of the supinator muscle to exit distally as the PIN. Anatomic landmarks could facilitate diagnosis and treatment of radial tunnel syndrome and aid in the injection and decompression of the radial nerve. Methods: Eighteen cadaveric arms were used to identify anatomic landmarks to facilitate location of the PIN. The landmarks used include the palpable proximal radial edge of the radial head, proximally, and the mid-width of the wrist, distally. The skin was incised along this longitudinal line through the fascia. Deep within this plane the PIN was identified exiting the distal edge of the superficial portion of the supinator muscle. The proximal and distal edges of the supinator muscle were measured from the proximal radial aspect of the radial head. In addition, the course of the DBRN was appreciated proximal and distal to the superficial part of the supinator muscle. Results: The PIN was identified to exit the superficial part of the supinator muscle at an average distance of 7.4 ± 0.4 cm distal to the proximal radial aspect of the radial head. Distal to the distal edge of the supinator muscle, the PIN passed along a longitudinal vector from the radial head to the mid-width point of the wrist. From within the supinator muscle the DBRN courses retrograde in an oblique direction toward the lateral edge of the distal most part of the biceps tendon. Conclusion: The anatomic landmarks of the radial head and the mid-width of the dorsal wrist can be used to predict the course and location of the PIN. The DBRN can be predicted to enter the superficial part of the supinator muscle approximately 3.5 cm distal to the radial head, and the PIN is predicted to exit the supinator at 7.5 cm distal to the radial head.