Anatomy of the Coracobrachialis and the Musculocutaneous Nerve

Courtesy: Prof Nabil Ebraheim, University of Toledo, Ohio, USA

The coracobrachialis muscle arises from the tip of the coracoid process and inserts into the middle third of the medial border of humeral shaft. The muscle may have a conjoint tendon with the short head of the biceps muscle. The muscle lies lateral to the pectoralis minor muscle. Close to the origin of coracobrachialis muscle is the origin of the coracoclavicular ligaments. The innervation of the coracobrachialis muscle comes from the musculocutaneous nerve which is close to the muscle . It flexes and adducts the arm at the shoulder joint.

The musculocutaneous nerve is the terminal branch of lateral cord of brachial plexus. It pierces the coracobrachialis about 3-8cm distal to the coracoid where it then gives a branch to the coracobrachialis muscle (some studies show that the nerve may be 1-5cm from the coracoid). The nerve runs between the biceps and the brachialis muscle on the anterior compartment of the forearm. The muscles innervated by the musculocutaneous nerve are coracobrachialis , biceps brachii and brachialis muscles. It also give the lateral antebrachial cutaneous nerve with its anterior and posterior divisions. It is the primary nerve supply of the muscles of the anterior compartment of the upper arm. It also supplies sensation to the lateral half of the forearm.

The musculocutaneous nerve is close to approaches of anterior shoulder especially with retraction of the conjoint tendon of the coracobrachialis and short head of the biceps. When the musculocutaneous nerve is injured, we may not be able to measure the deficit except for decreased sensation on the area supplied by the lateral antebrachial cutaneous nerve, which is a terminal branch that will give sensation to the forearm. Occasionally, coracoid osteotomy is done to enhance exposure to the shoulder joint and the conjoint tendon can be easily retracted without compromising the musculocutaneous nerve.
The lateral antebrachial cutaneous nerve could be injured during distal biceps repair.