Dr. Ebraheim’s educational animated video describes the anatomy of the musculocutaneous nerve.
Musculocutaneous nerve innervates the biceps brachi muscle and skin sensation to the lateral half of the forearm. The Musculocutaneous nerve arises from the lateral cord of the brachial plexus. It is the primary nerve supply of the muscles of the anterior compartment of the upper arm and it supplies sensation to the lateral half of the forearm. The Musculocutaneous nerve is the distal contribution of the lateral cord of the brachial plexus. It predominately arises from the C5, C6 level with some contribution from C7. It contains fibers from the upper trunk. Musculocutaneous nerve lies lateral to the axillary artery and starts at the lower border of the pectoralis minor muscle. In the axilla the nerve travels distally and laterally to pierce the coracobrachialis muscle proximally 30-8 cm distal to the tip of the coracoid. Musculocutaneous nerve innervates the coracobrachialis muscle. After passing through the deep to the coracobrachialis muscle, the nerve continues distally, superficial to the brachialis muscle and deep to the lateral border of the distal biceps muscle. The brachialis muscle is supplied by two nerves, the Musculocutaneous nerve and the radial nerve. The radial nerve supplies a small portion of the lateral aspect of the brachialis muscle. Around the elbow region, the nerve pierces the superficial fascia lateral to the distal biceps tendon insertion and the nerve terminates as the lateral antebrachial cutaneous nerve, supplying the lateral half of the forearm.
The function of the biceps muscle: it flexes the elbow and supinates the forearm when the elbow is flexed.
Musculocutaneous nerve palsy
It will cause weakness of elbow flexion, weak forearm supination and numbness in the anterolateral forearm that stops at the wrist.
Differential diagnosis:
Rupture of the distal biceps tendon: that can be diagnosed by MRI or clinically by performing the hook test.
C6 radiculopathy: the patient will complain of radicular pain and numbness in the thumb and index finger. Other muscles associated with C6 will be affected.
The lateral antebrachial cutaneous nerve
This nerve can be injured from venipuncture in the cubital fossa. It can also be injured during repair of the distal biceps tendon rupture. This nerve must be visualized and retracted to avoid its injury. If you can’t find the nerve during repair of the distal biceps tendon rupture, try to find proximally under the biceps and in front of the brachialis and track the nerve distally to find its location.
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12 ноя 2015
