The three nerves of the hand: median, ulnar and radial

1. Musculocutaneous nerve

It pierces coracobrachialis and runs between biceps and brachialis, supplying the elbow flexors, then ends as the lateral cutaneous nerve of the forearm.

Surgeon’s corner: It enters coracobrachialis only 5–8 cm below the coracoid: excessive medial retraction of the conjoint tendon in shoulder surgery stretches it.

2. Radial nerve in the spiral groove

The radial nerve spirals around the back of the humerus in the radial groove with the deep brachial artery, between the heads of triceps, then pierces the lateral intermuscular septum to the front of the elbow.

Surgeon’s corner: Humeral shaft fractures, especially spiral fractures of the distal third (Holstein–Lewis), injure the radial nerve: wrist drop. Find and protect it in every posterior or lateral approach to the humerus.

3. Median nerve

The median nerve runs with the brachial artery down the medial arm, crosses the elbow medial to the biceps tendon, runs through the forearm between the flexor muscles and enters the hand through the carpal tunnel under the flexor retinaculum.

Surgeon’s corner: Carpal tunnel syndrome: numb thumb, index and middle finger, worse at night; thenar wasting late. Release the flexor retinaculum on the ulnar side of the palmaris longus line to protect the motor (recurrent) branch.

4. Ulnar nerve

The ulnar nerve passes behind the medial epicondyle (the funny bone) in the cubital tunnel, runs down the forearm under flexor carpi ulnaris with the ulnar artery and enters the hand through Guyon’s canal.

Surgeon’s corner: Cubital tunnel syndrome is the second commonest nerve entrapment. Medial K-wires in a child’s supracondylar fracture can skewer the ulnar nerve: make a small incision or use lateral wires only.

5. The two arteries of the forearm

The brachial artery divides at the elbow into the radial artery (under brachioradialis, then lateral to flexor carpi radialis at the wrist) and the ulnar artery (deep, then with the ulnar nerve).

Surgeon’s corner: The volar (Henry/FCR) approach to the distal radius goes through the sheath of flexor carpi radialis, keeping the radial artery laterally and the median nerve medially.