The coracobrachialis is a slender muscle running from the coracoid process to the medial humerus, sandwiched between the short biceps head anteriorly and the brachialis laterally. It is the smallest of the three coracoid-origin muscles and its mechanical contribution to arm movement is modest, but it carries unique clinical significance because the musculocutaneous nerve pierces directly through it on its way to the forearm.
| Origin | Apex of the coracoid process of the scapula, sharing this attachment with the short head of the biceps brachii |
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| Insertion | Medial surface of the humeral shaft at its midpoint |
| Nerve Supply | Musculocutaneous nerve (C5, C6, C7), which pierces directly through the muscle belly |
| Blood Supply | Brachial artery |
| Actions | Flexion of the arm at the shoulder; Adduction of the arm; Passive resistance to inferior humeral head translation |
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It contributes to shoulder flexion and adduction and its medial humeral attachment resists inferior translation of the humeral head during loading activities such as carrying heavy bags.
Coracobrachialis syndrome, where the musculocutaneous nerve is compressed within the muscle belly, produces forearm paraesthesia in the lateral cutaneous nerve distribution combined with biceps and brachialis weakness, closely mimicking a biceps tendon problem. The muscle is an important surgical landmark in the deltopectoral approach to the shoulder and in axillary lymph node dissection. Hypertrophy from heavy resistance training occasionally contributes to nerve compression.
The coracobrachialis is palpable in the medial upper arm between the anterior biceps and the posterior triceps, becoming firm with resisted shoulder flexion and adduction with the elbow held straight.
Compression of the nerve within the coracobrachialis belly from direct trauma or hypertrophy, producing lateral forearm paraesthesia and biceps weakness that is distinguished from biceps tendon pathology by the sensory loss in the nerve's cutaneous distribution.
