Posterior interosseous nerve

Anatomy and function of the posterior interosseous nerve

The posterior interosseous nerve is a branch of the radial nerve that supplies the extensor muscles of the forearm. It is primarily responsible for the motor innervation of these muscles, which are involved in the extension of the wrist and fingers.

Diagram of the posterior interosseous nerve and its branches.

Anatomy

The posterior interosseous nerve originates from the radial nerve, which is a major nerve of the upper limb. The radial nerve itself arises from the brachial plexus, specifically from the posterior cord. After the radial nerve passes through the radial groove of the humerus, it divides into a superficial branch and a deep branch. The deep branch continues as the posterior interosseous nerve.

The nerve enters the forearm by passing through the supinator muscle, a muscle that assists in the supination of the forearm. As it emerges from the supinator, it travels along the posterior aspect of the interosseous membrane, which is a fibrous sheet connecting the radius and ulna bones of the forearm.

Function

The primary function of the posterior interosseous nerve is to provide motor innervation to the extensor muscles of the forearm. These muscles include:

• Extensor carpi radialis brevis
• Extensor digitorum
• Extensor digiti minimi
• Extensor carpi ulnaris
• Abductor pollicis longus
• Extensor pollicis brevis
• Extensor pollicis longus
• Extensor indicis

These muscles are responsible for extending the wrist and fingers, as well as abducting the thumb.

Clinical Significance

Injury to the posterior interosseous nerve can result in a condition known as posterior interosseous nerve syndrome. This condition is characterized by weakness or paralysis of the extensor muscles of the forearm, leading to difficulty in extending the wrist and fingers. It can be caused by trauma, compression, or entrapment of the nerve, often at the level of the supinator muscle.

Symptoms of posterior interosseous nerve syndrome include wrist drop, where the patient is unable to extend the wrist, and weakness in finger extension. Diagnosis is typically made through clinical examination and may be confirmed with electromyography (EMG) studies.

Related pages

• Radial nerve
• Brachial plexus
• Extensor muscles of the forearm
• Wrist drop