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Musculocutaneous Nerve

nervus musculocutaneus

The musculocutaneous nerve supplies the three muscles of the anterior upper arm and continues as the lateral cutaneous nerve of the forearm. Its unique feature is that it pierces the coracobrachialis belly immediately after entering the arm from the axilla, making this muscle a potential entrapment site. It is the nerve tested when assessing biceps function and the C5 and C6 nerve roots.

Region: Upper Arm

Anatomical Data

Origin, Insertion & Supply

Origin	Lateral cord of the brachial plexus (C5, C6, C7)

Clinical Relevance

Clinical Notes

Isolated musculocutaneous nerve injury is uncommon but produces biceps and brachialis weakness causing elbow flexion and supination weakness, combined with lateral forearm numbness. The biceps tendon reflex is absent or diminished. Coracobrachialis syndrome, entrapment within the muscle, produces lateral forearm paraesthesia combined with elbow flexion weakness and is distinguished from biceps tendon pathology by the sensory component. Musculocutaneous nerve injury can occur during heavy bench press exercises or aggressive coracoid-based shoulder procedures.

Pathology

Common Injuries & Conditions

Musculocutaneous Nerve Injury

Elbow flexion and supination weakness with lateral forearm numbness from nerve damage at any point along its course, with coracobrachialis entrapment being the most common site.