Posterior interosseous nerve of forearm

At a glance

English

Posterior interosseous nerve of forearm

Latin (TA2)

Nervus interosseus posterior antebrachii

System

Nerve

Region

Upper limb

Side

Paired, left and right

About the posterior interosseous nerve of forearm

The posterior interosseous nerve is the name the deep radial branch takes once it has passed through the supinator muscle and reached the back of the forearm. The radial nerve divides in front of the lateral epicondyle into a superficial sensory branch and this deep, mainly motor branch. The deep branch supplies extensor carpi radialis brevis and supinator, then enters supinator under a fibrous arch at its upper edge, the arcade of Frohse, and winds round the lateral side of the neck of the radius within the muscle. On leaving it, the nerve is noticeably smaller. Its fibres come chiefly from C7 and C8.

On the back of the forearm the nerve runs down between the superficial and deep layers of extensor muscles, accompanied by the posterior interosseous artery. At the lower border of extensor pollicis brevis it passes deep to extensor pollicis longus and lies on the interosseous membrane. It continues to the back of the wrist, where it ends in a small swelling, sometimes called a pseudoganglion, that sends twigs to the ligaments and joints of the carpus.

Its muscular branches supply extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus and extensor indicis. Brachioradialis, extensor carpi radialis longus and anconeus are supplied higher up by the radial nerve itself. The nerve has no skin territory, but it carries position sense from the wrist and the distal radioulnar joint.

Because it is purely motor, damage to the posterior interosseous nerve causes weakness without numbness. The patient cannot straighten the fingers at the knuckles or lift the thumb, giving finger drop, while the wrist can still be extended, drifting towards the radial side because extensor carpi radialis longus works but extensor carpi ulnaris does not. The nerve can be trapped at the arcade of Frohse, pressed by a ganglion, lipoma or inflamed elbow joint, or injured by fractures and dislocations of the radial head, including the Monteggia injury. Surgeons approaching the radial neck turn the forearm into pronation to move it away.

Course and supply

Arises from

The deep radial branch as it continues beyond the supinator muscle (fibres mainly C7, C8).

Ends in

Ends on the back of the wrist in a small swelling that supplies the carpal joints and ligaments.

Supplies

Motor to extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, abductor pollicis longus, extensor pollicis brevis and longus, and extensor indicis; sensory to the wrist and distal radioulnar joint capsules.