Anatomy and internal topography of the musculocutaneous nerve: the nerves to the biceps and brachialis muscle.

One hundred twelve musculocutaneous nerves from 56 cadavers were examined to determine branching patterns of innervation and internal neurotopography. There were 3 distinct types of branching patterns for biceps innervation: in 62%, there was 1 branch only; in 33%, 2 branches; and in 5%, 3 branches. The origin of the first branch averaged 130 mm from the acromion regardless of branching type. The maximum distance between the first and second branch was 53 mm. In 92%, there was only 1 branch to the brachialis muscle. It always emerged from the main trunk distal to the nerve to the biceps and averaged 170 mm from the acromion. Internal topography was studied from 1-mm-thick serial sections of the musculocutaneous nerve in 5 fresh cadaver arms. The group of fasciculi of the nerve to the biceps, the nerve to the brachialis, and the lateral cutaneous nerve of the forearm were constantly located from lateral to medial. The fasciculi of the nerve to the biceps traveled proximally in the musculocutaneous nerve for an average distance of 63 mm.