The musculocutaneous nerve and its branches to the biceps and brachialis muscles.

The musculocutaneous nerve and its motor branches to the biceps and brachialis were dissected and studied under the operating microscope in 24 fresh-frozen cadaveric specimens. The motor branch to the biceps exits from the musculocutaneous nerve at 119 mm distal to the coracoid process. Anatomic variations were seen in the innervation of the two heads of the biceps. A common primary motor branch that bifurcates to supply the two heads was seen in 20 specimens (type I). Two specimens were observed to have two separate primary branches originating from the main musculocutaneous nerve trunk to individually supply each head of the biceps (type II). The third variation, two specimens (type III), was observed in two specimens to be similar to type I, but with an additional distal motor branch innervating the common belly of the biceps muscle. The motor branch to the brachialis muscle exists from the musculocutaneous nerve 170 mm distal to the coracoid process. A single primary motor branch (type I) was seen in 23 specimens, and 1 specimen (type II) showed two separate primary motor branches innervating the muscle. The motor branches to the biceps and brachialis muscles may be dissected proximally from their points of exit from the main trunk of the musculocutaneous nerve for a mean distance of 44 mm and 53 mm, respectively. This information can be used by surgeons who elect to suture intercostal nerves to the motor branches of the biceps and brachialis muscles for elbow flexion in brachial plexus injuries.