Musculocutaneous nerve transit through a supernumerary head of the biceps brachii: implications for lateral antebrachial cutaneous and musculocutaneous nerve entrapments, diagnosis, and treatment

Abstract

The lateral antebrachial cutaneous nerve (LACN) can be entrapped by the biceps tendon or bicipital aponeurosis at the cubital fossa, and the musculocutaneous nerve (MCN) can be compressed as it penetrates the coracobrachialis. Either condition can result in pain in the anterolateral elbow region and dysesthesia of the lateral forearm. These entrapment syndromes are treated either conservatively or by surgical decompression of the LACN by incision or resection of the biceps tendon or bicipital aponeurosis. We describe an unusual anatomical variation of a musculocutaneous nerve that penetrates a third head of the biceps brachii before continuing as the lateral antebrachial cutaneous nerve. Compression of the MCN by such a supernumerary biceps head could result in a pattern of symptoms similar to LACN entrapment at the elbow or MCN entrapment at the shoulder. Given that the frequency of supernumerary biceps heads has been reported to be as high as 12% in the general population, this etiology should be considered by clinicians in the differential diagnosis and treatment of these entrapment syndromes.