The Branching Pattern and Internal Topography of the Musculocutaneous Nerve
Authors: Elgammal Yehia , Frolov Andrey , Martin John R. 
Published: April 2020

BackgroundPrevious research on the musculocutaneous nerve (MCN) has focused on its motor and sensory branching pattern. Defining the branching pattern is important for selective neurectomy in the treatment of elbow flexor spasticity (EFS). Very limited data, however, exists regarding its internal topography, which is important for surgical procedures. Several neurotization techniques of the MCN, such as intercostal nerve transfer, rely on the location of motor and sensory fascicles of the MCN from the lateral cord. The purpose of this study is to confirm the MCN branching pattern and define its internal topography.ResultsThe study was performed on 15 arms (9 left and 6 right) in 12 Caucasians cadavers. Branches of the MCN nerve to the coracobrachialis, biceps brachii and brachialis muscles were assessed and presented as a percentage of the distance from the coracoid process to the medial epicondyle. The internal topography of each fasciculus was identified at proximal, middle and distal levels following blunt intraneural dissection from the respective branch termination up to the lateral cord. It was found that the coracobrachialis muscle was innervated by 1–3 primary branches arising from MCN at an average of 17.7% of the arm length. The biceps brachii was innervated by 1–2 primary branches arising at an average 45% of the arm length. The brachialis was innervated by a single branch arising at an average 60% of the arm length. Regarding its internal topography, the lateral cutaneous nerve to the forearm occupied the medial and anteromedial one fourth at proximal and middle levels, but the lateral and posterolateral one fourth at the distal level. The branches to the coracobrachialis and biceps brachii occupy the anterior and anterolateral one fourth at the proximal level, and the branches to the brachialis occupy the lateral and posterolateral one fourth at proximal and middle levels, and the medial and posteromedial one fourth at the distal level.ConclusionsCompared to the respective data found in the literature, our present results indicate that the branching points of the nerves to coracobrachialis, biceps brachii, and brachialis are relatively constant at approximately 20%, 40%, and 60% respectively, of the distance between the coracoid process and the medial epicondyle. Additionally, regarding the internal topography, our results indicate that while at the distal level the lateral cutaneous nerve to the forearm was located lateral and the brachialis branch was located medial, at the proximal level of MCN the nerves to the coracobrachialis, biceps brachii and brachialis occupy the lateral three fourths and lateral cutaneous nerve of the forearm occupies the medial one fourth. Based on the data obtained, it appears that the lateral half of the proximal and middle levels and the medial half of distal level of MCN would be the preferred site for any motor nerve transfer. These findings are important for the development of more efficient microsurgical procedures to treat EFS and for neurotization of the MCN.Support or Funding InformationCenter for Anatomical Science and Education, Department of Surgery, Saint Louis University School of Medicine