Anatomical study of the musculocutaneous nerve branching pattern: application for selective neurectomy in the treatment of elbow flexors spasticity

Purpose Spastic flexion deformity of the elbow is mainly mediated by the biceps brachii and the brachialis muscles, innervated by the musculocutaneous nerve. Selective neurectomy of the musculocutaneous nerve showed promising results to relieve excessive spasticity in the long term but lacks of a consensual surgical strategy. The aim of the study was to describe the distal branching pattern of the motor branches of the musculocutaneous nerve in an attempt to develop guidelines for surgery. Methods Sixteen arms of fresh cadaver specimen were dissected. We recorded the site of each primary and terminal motor branch as a percentage of the distance from the coracoid process to the lateral epicondyle. Results The biceps muscle was innervated by one to five primary motor branches. The first branch emerged from the nerve at an average of 37.1 % of the arm length, and the most distal terminal branch at 55.7 %. The brachialis muscle received one to three primary branches. The first branch exited the nerve at an average of 51.7 % of the arm length and the last terminal branch at 69.3 %. The average number of terminal branches dedicated to the biceps and the brachialis muscles were, respectively, 7.9 and 6.5. Conclusions According to our findings, we recommend to dissect the musculocutaneous nerve between 18 and 75 % of the distance between the coracoid process and the lateral epicondyle to identify the motor terminal branches to the biceps brachii and the brachialis muscle, sparing sensory branches.