Classifying Musculocutaneous Nerve Variations

A total of 56 upper limbs from fetuses and adult cadavers were dissected to record anatomical variations in the musculocutaneous nerve (MC). A systematic literature review was performed to identify current classifications of MC variations. Communications were seen between the MC and median nerves in 53.6% of the dissections from which 84.6% were proximal, 7.7% distal, and 7.7% had one proximal and one distal communication to the point of entry of the MC into coracobrachialis muscle. In six out of 54 dissections where the MC was present, the nerve did not pierce the coracobrachialis muscle. In two cases, the MC was absent and in one case the MC and the median nerve had a distal origin. This article describes current classifications of MC variations and their problems. A new classification is proposed combining preexisting ones into an integrated and more detailed overview. Clinical manifestations of isolated MC injury with and without the presence of anatomical variations are thoroughly discussed. The knowledge of these variations will allow physicians to correctly interpret anomalous innervation patterns of the upper limb.