Musculocutaneous nerve

1. What nerve roots contribute to the musculocutaneous (msc) nerve?
2. What muscles are innervated by the msc nerve? What sensory nerves are given off by the the msc nerve?
3. How is the msc nerve usually injured?
4. What is the presentation of msc nerve injury?
5. What are the EMG/NCS findings?

Answers:
1. C5, C6, C7, which become the upper trunk, then lateral cord.
2. Coracobrachialis, biceps brachii, brachialis. The lateral antebrachial cutaneous nerve innervates the lateral forearm.
3. Distal injury is more common than proximal. It can be injured by entrapment prox from the coracobrachialis, or by gunshot wounds, shoulder dislocation, or phlebotomy.
4. Elbow flexion weakness and abnormal sensation over lateral forearm. Coracobrachialis usually spared.
5. SNAP abnormal in lateral antecubital cutaneous nerve. CMAP abnormal to biceps. EMG abnormal in biceps and brachialis.