Spinal nerve origins of the muscular branches of the radial nerve: an electrophysiological study.

BACKGROUND: In injuries of the lower brachial plexus, finger flexion can be restored by nerve or tendon transfer. However, there is no technique that can guarantee good recovery of finger and thumb extension. OBJECTIVE: To determine the spinal nerve origins of the muscular branches of the radial nerve and identify potential intraplexus donor nerves for neurotization of the posterior interosseous nerve in patients with lower brachial plexus injuries. METHODS: An intraoperative electrophysiological study was carried out during 16 contralateral C7 nerve transfers. The compound muscle action potential of each muscle innervated by the radial nerve was recorded while the C5-T1 nerves were individually stimulated. RESULTS: The triceps brachii muscle primarily received root contributions from C7. The C5 and C6 nerve roots displayed greater amplitudes for the brachioradialis and supinator muscles compared with those of the C7, C8, and T1 nerve roots (P < .05). The extensor carpi radialis branch was innervated by C5, C6, and C7, and no significant differences were detected between them (P > .05). The amplitudes obtained for the extensor digitorum communis branch were the largest from C7 and C8, without a significant difference between them (P > .05), whereas the amplitudes of the extensor carpi ulnaris and extensor pollicis longus were largest from the C8 root (P < .05). CONCLUSION: The supinator muscle branch is likely the best donor nerve for the repair of lower brachial plexus injuries affecting muscles that are innervated by the posterior interosseous nerve.