Anterior interosseous nerve of forearm

At a glance

English

Anterior interosseous nerve of forearm

Latin (TA2)

Nervus interosseus anterior antebrachii

System

Nerve

Region

Upper limb

Side

Paired, left and right

About the anterior interosseous nerve of forearm

The anterior interosseous nerve, sometimes called the volar interosseous nerve, is the largest branch of the median nerve in the forearm. It leaves the back of the median nerve just below the elbow, usually as the parent nerve passes between the two heads of pronator teres, and carries fibres mainly from the lower cervical segments of the plexus.

The nerve sinks deep and runs straight down the front of the interosseous membrane, together with the anterior interosseous artery. It lies in the groove between flexor pollicis longus on the radial side and flexor digitorum profundus on the ulnar side, giving branches to both as it goes. Near the wrist it passes behind pronator quadratus, supplies it, and ends in fine articular twigs.

It is chiefly a motor nerve to the deep layer of the front of the forearm. It supplies all of flexor pollicis longus, which bends the tip of the thumb; the lateral part of flexor digitorum profundus, which bends the tips of the index and usually the middle fingers; and pronator quadratus, the main pronator when the elbow is bent. The ulnar half of profundus, like flexor carpi ulnaris, belongs to the ulnar nerve. The nerve has no skin territory, but its terminal twigs carry sensation from the distal radioulnar, radiocarpal and intercarpal joints.

Injury, whether from a penetrating wound, compression near the elbow or, most often, an inflammatory neuritis, produces anterior interosseous nerve syndrome. The patient cannot bend the end joints of the thumb and index finger, so trying to make an OK sign gives a flattened pinch instead of a round circle; pronation with the elbow flexed is weak, and skin sensation is normal. Treatment is usually rest and splinting, with surgical release if recovery fails. In pronator syndrome the whole median nerve is compressed, not just this branch. Because its distal part is expendable, surgeons can transfer the end of this nerve to the deep branch of the ulnar nerve to restore the small hand muscles after ulnar nerve injury.

Course and supply

Arises from

Arises from the posterior side of the median nerve in the upper forearm, near the two heads of pronator teres.

Ends in

Ends behind pronator quadratus in branches to that muscle and articular twigs to the wrist and distal radioulnar joint.

Supplies

Motor to flexor pollicis longus, the lateral part of flexor digitorum profundus, and pronator quadratus; sensory to the distal radioulnar, wrist and carpal joints, with no skin supply.

Blood supply

Accompanied along its whole course by the anterior interosseous artery.