Origination of the brachialis branch of the musculocutaneous nerve: An electrophysiological study

OBJECTIVE: To test an innovative method to study the origin of a specific nerve or of the nerve fibers innervating a given muscle on the healthy upper limb of a human being and to find the rationale for the brachialis branch of musculocutaneous nerve transfer. METHODS: An intraoperative electrophysiological study was conducted comprising 27 cases of contralateral C7 transfer. The goal of the study was to record compound muscle action potential of the brachialis muscle while various nerve roots of the brachial plexus were stimulated. RESULTS: Analysis of compound muscle action potential suggested that the brachialis branch of the musculocutaneous nerve is composed of fibers from the C5, C6, and C7 nerve roots and that the C5 and C6 nerve roots are the major origin for the brachialis branch of musculocutaneous nerve fibers. CONCLUSION: The technique proposed here was a more direct and functional method of tracing the origin of a specific nerve or of the nerve fibers innervating a given muscle on the healthy upper limb of a live patient.