Anatomic study in cadaver of the motor branch of the musculocutaneous nerve

Abstract

This study of 80 cadavers demonstrates that the anatomic position of the motor branch of the musculocutaneous nerve with respect to that of the sensitive branch of the same nerve is lateral in more than 88% of cases in humans. The distance from plexus to the separation into the motor and sensitive fascicles was 8-9 cm long. Given the lateral position of the motor component of the musculocutaneous nerve, the nerves that are going to be used to neurotize this area can be directed so as to increase the efficacy of the results for the flexor function of the arm. Introduction: Brachial plexus lesions produce great morbidity and are relatively frequent in young adults. Innervating the coracobrachial, biceps and anterior brachial muscles, the musculocutaneous nerve is one of the priorities for nerve neurotization when plexus root avulsion occurs because it is essential for arm flexion. This nerve has both a motor and sensitive component, and the anatomic positions of the two components have not been much studied. When performing a neurotization anastomosis to the musculocutaneous nerve, being able to identify the motor component of the graft and attach it to the motor component of the musculocutaneous nerve could avoid a loss of many motor axons which would otherwise occur if the graft were attached to the sensitive component. Objective: The present paper is based on a topographic anatomic study to locate and obtain the objective positioning of the motor branch of the musculocutaneous nerve in humans, as well as measure its length from the origin in the brachial plexus to the separation of both fascicles into branches. Material and Methods: The study was performed in 40 cadavers, dissecting the musculocutaneous nerve along its course and measuring the distance from its emergence from the plexus until the separation between its motor and sensitive branches in both arms so as to be able to determine the positioning of the motor fascicle with respect to the sensitive fascicle. Results: The distance from plexus to the separation into the motor and sensitive fascicles was 8.8 cm on the left side and 8.95 cm on the right side. The position of the motor branch with respect to the sensitive branch was lateral in more than 85% of the studied nerves, all the way from its origin in the brachial plexus until the definitive separation between both branches, on both the right and the left sides. Conclusion: If the nerves that are to be used for neurotization of the musculacutaneous nerve are directly taken to the lateral fascicle of that nerve, which is generally the motor component, the treatment should be effective and should avoid the loss of motor axons resulting from anastomosing to the sensitive fascicle. © 2011 Springer-Verlag/Wien.