Innervation

The anterior interosseous nerve innervates 2.5 muscles:

  • Flexor pollicis longus
  • Pronator quadratus
  • The lateral half of flexor digitorum profundus (lateral two out of the four tendons)

These muscles are in the deep level of the anterior compartment of the forearm.


Figures 1 and 2. Two views of the anterior interosseous nerve

Injury

A branch of the median nerve, the anterior interosseous nerve can be affected by either direct penetrating injury or compression in a fashion similar to carpal tunnel syndrome. The compression neuropathy is referred to as anterior interosseous syndrome. As might be expected, the symptoms involve weakness in the muscle innervated by the anterior interosseous nerve, including the flexor digitorum profundus muscle to the index (and sometimes the middle) finger, the flexor pollicis longus muscle to the thumb, and the pronator quadratus of the distal forearm. As opposed to carpal tunnel syndrome, the anterior interosseous nerve has no sensory fibers and therefore no numbness associated with anterior interosseous syndrome. Non-surgical treatment consists of splinting, proximal tissue massage and anti-inflammatory drugs. Surgical treatment consists of releasing the compression on the nerve from surrounding structures. Pronator syndrome is similar, but involves the anterior interosseous nerve and the median nerve proper.

Discussion

The anterior interosseous nerve (volar interosseous nerve) is a branch of the median nerve that supplies the deep muscles on the front of the forearm, with the exception of the ulnar half of the flexor digitorum profundus.

It accompanies the anterior interosseous artery along the front of the interosseous membrane of the forearms, in the interval between the flexor pollicis longus and flexor digitorum profundus, supplying the whole of the former and the radial half of the latter, and ending below in the pronator quadratus and wrist joint.

Many texts, for simplicity’s sake, consider this nerve part of the median nerve.

Attachments: