Anatomical feasibility of transferring supinator motor branches to the posterior interosseous nerve in C7–T1 brachial plexus palsies

OBJECT: In C7-T1 palsies of the brachial plexus, shoulder and elbow function is preserved, but finger motion is absent. Finger flexion has been reconstructed using tendon or nerve transfers. Finger extension has been restored ineffectively by attaching the extensor tendons to the distal side of the dorsal radius (that is, tenodesis). In these types of nerve palsy, supinator muscle function is preserved because innervation stems from the C-6 root. In the present study, the authors investigated the anatomy and the feasibility of transferring the supinator motor branches to the posterior interosseous nerve. Sacrifice of the supinator motor branches does not abolish supination because biceps muscle function is preserved in lower-type injuries of the brachial plexus. METHODS: The posterior interosseous nerve was dissected in 20 formalin-fixed forearms. Through posterior forearm access, the posterior interosseous nerve and its motor branches to the supinator muscle were dissected. Specimens were removed for histological study. RESULTS: In the vicinity of the supinator muscle's proximal margin (that is, the Frohse arcade), 2 nerve branches arose laterally and medially from the posterior interosseous nerve to innervate the superficial and deep heads of the supinator muscle, respectively. The supinator motor nerves, when divided, could be coapted directly to the posterior interosseous nerve. The number of myelinated fibers in the supinator motor branches corresponded to 70% that of the posterior interosseous nerve. CONCLUSIONS: The supinator motor nerves can be transferred directly to the posterior interosseous nerve to restore thumb and finger extension in patients with C7-T1 brachial plexus lesions.