A novel classification of musculocutaneous nerve variations: The relationship between the communicating branch and transposed innervation of the brachial flexors to the median nerve.

The musculocutaneous nerve innervates the brachial flexors; i.e., the coracobrachialis, biceps brachii, and brachialis. The musculocutaneous and median nerve sometimes share a communicating branch and also muscular branches to brachial flexors are sometimes transposed to median nerve. Because these variations constitute a potentially important clinical and surgical issue, we evaluated 130 upper limbs of 65 cadavers and 184 cases of musculocutaneous and median nerve variations in the literature and devised a novel system of classification that covers each pattern of variation. Our proposed classification was applicable in all of our cases and those previously reported. In addition, transposed innervation of the brachial flexors from the musculocutaneous nerve to the communicating branches was observed in one limb in our case series. In this case and all previously reported cases of transposed innervation of the brachial flexors, communicating branches between the musculocutaneous and median nerve were found and no brachial flexor branch arose from the musculocutaneous nerve distal to the communicating branches. Consequently, we established that, as per our novel classification, all patterns of communicating branches could be classified into five types and the patterns of transposed innervation of the brachial flexors into three types.