Radial nerve

At a glance

English

Radial nerve

Latin (TA2)

Nervus radialis

System

Nerve

Region

Upper limb

Side

Paired, left and right

About the radial nerve

The radial nerve is the bigger of the two nerves in which the posterior cord ends, and it carries fibres from C5 to T1. It begins posterior to the axillary artery's third part and passes downwards behind the brachial artery. It then leaves the axilla backwards through the triangular interval below teres major, between the long head of triceps and the humerus, together with the profunda brachii artery.

Behind the humerus the nerve spirals downwards and laterally in the radial groove, between the lateral head and the medial head of triceps and in direct contact with the bone. Below the deltoid tuberosity it passes through the lateral intermuscular septum into the front of the arm, where it lies deeply between brachialis and brachioradialis. In front of the lateral epicondyle it divides into its two terminal branches. The superficial branch is sensory and runs down the forearm under brachioradialis before turning onto the dorsum of the wrist and hand. The deep branch is motor; it passes through supinator, winding round the radius, and continues on the back of the forearm as the posterior interosseous nerve.

Before dividing, the nerve supplies triceps, anconeus, brachioradialis, extensor carpi radialis longus and part of brachialis, and gives cutaneous nerves to the back of the arm, the lower lateral arm and the back of the forearm. The deep branch adds extensor carpi radialis brevis and supinator, and the posterior interosseous nerve supplies the remaining extensors of the wrist, fingers and thumb and abductor pollicis longus. The superficial branch carries feeling from the thumb side of the hand's dorsum and the backs of the thumb, index, middle and radial half of the ring finger.

Radial nerve injuries are graded by level. Pressure in the axilla, from a crutch or from sleeping with the arm hung over a chair, can weaken triceps as well as causing wrist drop. A fracture of the humeral shaft can injure the nerve in the radial groove, leaving elbow extension intact but the wrist and fingers unable to extend. Damage at or below the elbow, from a radial head fracture or entrapment in supinator, gives finger drop without numbness. Pressure on the superficial branch near the wrist, by a tight watch strap for instance, causes only tingling on the back of the hand.

Course and supply

Arises from

The larger of the posterior cord's two end branches (C5 to T1), posterior to the axillary artery.

Ends in

Divides in front of the lateral epicondyle into the superficial branch and the deep branch, which continues as the posterior interosseous nerve.

Supplies

Motor to triceps, anconeus, brachioradialis and all extensors of the wrist, fingers and thumb, supinator and abductor pollicis longus; sensory to the back of the arm and forearm and the radial back of the hand.