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 |
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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.
The musculocutaneous nerve usually enters coracobrachialis several centimetres below the coracoid tip, although the distance varies and can be short, so the muscle is a landmark for protecting the nerve during the deltopectoral approach and coracoid surgery. Compression of the nerve within the muscle (coracobrachialis syndrome), occasionally from hypertrophy in heavy resistance training, causes lateral forearm paraesthesia with biceps and brachialis weakness. In the Latarjet procedure the coracoid tip is transferred with the conjoined tendon of coracobrachialis and short head of biceps attached, which acts as a sling over the lower subscapularis; excessive traction on the conjoined tendon can stretch the nerve. The muscle is also a landmark in axillary lymph node dissection.
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.
