Deep branch of radial nerve

At a glance

English

Deep branch of radial nerve

Latin (TA2)

Ramus profundus nervi radialis

System

Nerve

Region

Upper limb

Side

Paired, left and right

About the deep branch of radial nerve

The radial nerve is the largest branch of the brachial plexus's posterior cord, so its fibres come from spinal nerves C5 to T1. In front of the lateral epicondyle, at the level of the elbow, it divides into two terminal branches: a superficial branch that is sensory and a deep branch that is mainly motor. Some authors treat the deep branch and the posterior interosseous nerve as one nerve; others give the name posterior interosseous only to its lower continuation.

From its origin the deep branch curls backwards round the outer side of the upper radius, close to the neck of the bone. It does so by running through the supinator muscle, between its superficial and deep layers. At the upper edge of the superficial layer it passes under a fibrous arch, the arcade of Frohse, whose size varies between people. Emerging on the back of the forearm, it runs down between the superficial and deep groups of extensor muscles towards the middle of the forearm, much reduced in size, and continues as the posterior interosseous nerve on the interosseous membrane to the back of the wrist.

Before entering supinator it supplies extensor carpi radialis brevis and supinator itself. After emerging it supplies extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, abductor pollicis longus, extensor pollicis brevis and longus, and extensor indicis. It has no cutaneous territory, but its terminal part gives sensory fibres to the wrist and carpal joints.

Injury causes weakness of finger and thumb extension. Because extensor carpi radialis longus is supplied above the division, the wrist can usually still be lifted, though it drifts towards the radial side; wrist drop is more typical of higher injury to the radial nerve, as from compression in the armpit by crutches. Skin sensation is preserved. The nerve can be stretched or compressed when the elbow is injured, particularly in dislocation of the radial head, and can be trapped under the arcade of Frohse. Releasing that band has restored function in some cases.

Course and supply

Arises from

The radial nerve, in front of the lateral epicondyle at the elbow (fibres from C5 to T1, mainly C7 and C8, through the posterior cord).

Ends in

Continues down the back of the forearm as the posterior interosseous nerve, ending at the wrist and carpal joints.

Supplies

Motor to supinator and the extensor muscles of the back of the forearm, including extensor carpi radialis brevis; sensory to the wrist and carpal joints; no skin supply.