Anatomic Variations of the Musculocutaneous Nerve and Clinical Implications for Restoration of Elbow Flexion

Abstract

The restoration of elbow flexion is of primary importance in the management of patients with brachial plexus injuries. Superior functional outcomes via fascicle transfer from the ulnar and median nerves have resulted in this transfer being considered the mainstay of recovery of elbow flexion in patients with intact C8 and T1 function. An understanding of the anatomy of the musculocutaneous nerve (MCN) and its branching pattern is key while performing these transfers. A prospective cohort study was conducted in patients who underwent nerve transfer for the restoration of elbow flexion following a traumatic brachial plexus injury. The anatomic course and branching pattern of the MCN were recorded in eligible cases, both as a line diagram and using intraoperative photographs. One hundred fifty patients underwent nerve transfer for the restoration of elbow flexion following an injury to the brachial plexus. The MCN in 138 patients (92%) was found to pierce the coracobrachialis muscle before emerging lateral to it. One hundred thirty-four patients (89.3%) demonstrated the "classical" anatomy. One hundred fifteen patients (76.6%) had a single primary branch to the biceps, whereas 25 patients (16.6%) demonstrated a discrete motor branch to each head. One hundred thirty-three dissections (88.6%) revealed a single muscular branch to the brachialis arising posteromedially from the MCN, distal to the origin of the branch to the biceps brachii. Notable unreported variations, such as the MCN penetrating the biceps as it descended, multiple brachialis branches, and trifurcation of divisions of the MCN, were documented. Variations in MCN anatomy are quite common, and even unreported variations can be encountered. Exploration of the MCN and its branches for nerve transfers requires knowledge of these anatomic variations and vigilance to prevent inadvertent injuries while dissecting them for nerve transfer surgery.