MUSCULOCUTANEOUS NERVE
The musculocutaneous nerve and the axillary nerve are seldom injured; they are isolated from the brachial plexus, but are situated very close to it.
SURGICAL ANATOMY
The musculocutaneous nerve is one of the most variable nerves. In the majority of cases, it originates from the lateral cord of the brachial plexus but may also begin from the anterior branch of the superior trunk of the plexus before forming the cord. The level of its appearance is not permanent: it varies from the clavicle to the middle third of the arm. In some cases it is joined with the median nerve. Then the coracobrachial muscle is innervated directly by bundles from the lateral cord of the brachial plexus. In the beginning, the nerve goes inferiorly and slightly laterally to the brachial artery, perforating the coracobrachial muscle, and at the same time giving off small branches for its innervation. After that, it passes through the space between the biceps and brachialis, giving off branches for these muscles. Continuing its way inferiorly and laterally in the inferior third of the arm, it perforates the fascia just laterally to the biceps tendon and as a cutaneous nerve - the lateral cutaneous nerve of the forearm, it supplies the skin on the lateral surface of the forearm.
The projection of the nerve begins from the depths of the axillary fossa, laterally from the pulsations of the artery, and passes inferiorly and slightly laterally to the biceps tendon.
SURGICAL APPROACHES
The patient is placed in a supine position, and stretched aside. The exposure of the initial part of the musculocutaneous nerve is made in the same way as to the infraclavicular part of the brachial plexus in the axillary fossa.
The nerve is exposed relatively easily, revealing first the two initial branches of the median nerve that are found on the axillary artery, and after that, in following proximally the lateral branch, the beginning of the musculocutaneous nerve is reached.
For the distal parts approach, the incision of the skin, subcutaneous tissue and the fascia, is made along the internal border of the biceps. After that is penetrated between the biceps and brachialis, where the nerve is located. Between the two muscles the nerve runs obliquely downwards and slightly medially to laterally. At this place, it separates branches for the adjacent two muscles and as they are very thin, great care is needed for their preservation.