The posterior interosseous nerve (or dorsal interosseous nerve) is a nerve

Nerve

A peripheral nerve, or simply nerve, is an enclosed, cable-like bundle of peripheral axons . A nerve provides a common pathway for the electrochemical nerve impulses that are transmitted along each of the axons. Nerves are found only in the peripheral nervous system...

 in the forearm. It is the continuation of the deep branch of the radial nerve

Deep branch of the radial nerve

The deep branch of the radial nerve winds to the back of the forearm around the lateral side of the radius between the two planes of fibers of the Supinator, and is prolonged downward between the superficial and deep layers of muscles, to the middle of the forearm.Considerably diminished in size,...

, after this has crossed the supinator muscle

Supinator muscle

In human anatomy, the supinator is a broad muscle in the posterior compartment of the forearm, curved around the upper third of the radius. Its function is to supinate the forearm.-Terminology:...

. It is considerably diminished in size compared to the deep branch of the radial nerve

Deep branch of the radial nerve

The deep branch of the radial nerve winds to the back of the forearm around the lateral side of the radius between the two planes of fibers of the Supinator, and is prolonged downward between the superficial and deep layers of muscles, to the middle of the forearm.Considerably diminished in size,...

. The nerve fibers originate from cervical segments C7 and C8.

Course

It descends on the interosseous membrane

Interosseous membrane

An interosseous membrane is a broad and thin plane of fibrous tissue that separates many of the bones of the body. It is an important component of many joints.Interosseous membranes in the human body:* Interosseous membrane of the forearm...

, in front of the Extensor pollicis longus, to the back of the carpus

Carpus

In tetrapods, the carpus is the sole cluster of bones in the wrist between the radius and ulna and the metacarpus. The bones of the carpus do not belong to individual fingers , whereas those of the metacarpus do. The corresponding part of the foot is the tarsus...

, where it presents a gangliform enlargement from which filaments are distributed to the ligaments and articulations of the carpus.

Supply

It supplies all the muscles on the radial side and dorsal surface of the forearm, except the Anconæus, Brachioradialis

Brachioradialis

Brachioradialis is a muscle of the forearm that acts to flex the forearm at the elbow. It is also capable of both pronation and supination, depending on the position of the forearm...

, Extensor carpi radialis longus. In other words, it supplies the following muscles:

• Extensor carpi radialis brevis - deep branch of radial nerve
• Extensor digitorum
• Extensor digiti minimi
• Extensor carpi ulnaris
• Supinator muscle
  Supinator muscle
  In human anatomy, the supinator is a broad muscle in the posterior compartment of the forearm, curved around the upper third of the radius. Its function is to supinate the forearm.-Terminology:...
  
   - deep branch of radial nerve
• Abductor pollicis longus
• Extensor pollicis brevis
• Extensor pollicis longus
• Extensor indicis

Entrapment

The posterior interosseous nerve may be entrapped at the Arcade of Frohse

Arcade of Frohse

Arcade of Frohse, sometimes called the supinator arch, is the most superior part of the superficial layer of the supinator muscle, and is a fibrous arch over the posterior interosseous nerve....

, which is part of the Supinator muscle

Supinator muscle

In human anatomy, the supinator is a broad muscle in the posterior compartment of the forearm, curved around the upper third of the radius. Its function is to supinate the forearm.-Terminology:...

. Posterior interosseous neuropathy is purely a motor syndrome resulting in finger drop, and radial wrist deviation on extension.