Posterior Compartment of the Forearm

compartimentum antebrachii posterius

The posterior compartment of the forearm is the extensor-supinator compartment behind the radius, ulna and interosseous membrane. Its superficial and deep muscle layers extend the wrist, fingers and thumb and supinate the forearm, and all are supplied by the radial nerve and its deep branch, the posterior interosseous nerve.

Anatomical Data

Boundaries & Contents

Location	Back of the forearm.
Boundaries	Antebrachial fascia posteriorly Radius, ulna and interosseous membrane anteriorly Posterior border of the ulna medially
Contents	Brachioradialis and extensor carpi radialis longus and brevis (lateral group) Extensor digitorum, extensor digiti minimi, extensor carpi ulnaris Anconeus Supinator Abductor pollicis longus, extensor pollicis brevis and longus, extensor indicis Posterior interosseous nerve Posterior interosseous artery

Biomechanics

Function & Actions

Holds the muscles that extend the wrist and digits and supinate the forearm.

Clinical Relevance

Clinical Notes

Compartment syndrome here is less common than in the flexor compartment and is usually released through a dorsal incision after volar fasciotomy if pressures remain high. The posterior interosseous nerve winds around the radius in the supinator within this compartment and can be compressed or injured in proximal radius surgery. Many authors also describe the mobile wad (brachioradialis and the radial wrist extensors) as a separate lateral compartment.

Pathology

Common Injuries & Conditions

Posterior Interosseous Nerve Palsy

Injury or compression of the deep branch of the radial nerve in this compartment, causing finger and thumb drop without sensory loss.

Dorsal Forearm Compartment Syndrome

Raised pressure in the extensor compartment causing pain on passive wrist and finger flexion.

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