The extensor pollicis brevis is one of the muscles of the deep layer of the posterior compartment of the forearm.

The posterior compartment of the forearm consists of a superficial layer (7 muscles) and a deep layer (5 muscles).

There are 3 "pollicis" muscles in the deep layer which act on the thumb: abductor pollicis longus, extensor pollicis longus and extensor pollicis brevis.

All the muscles of the posterior compartment are innervated by the radial nerve.

The muscles of the deep layer include:

Origin
  • Posterior surface of the radius and adjacent interosseus membrane, distal to the origin of the abductor pollicis longus
Insertion
  • Dorsal surface of base of proximal phalanx of the thumb

It emerges between the extensor digitorum and extensor carpi radialis brevis muscles (superficial layer muscles) and accompanies the abductor pollicis longus within a groove on the posterlateral surface of the distal radius.

Innervation
  • Posterior interosseus nerve
Blood Supply
  • Posterior interosseus artery
  • Anterior interosseus artery
Action
  • Extension of the thumb at the carpometacarpal and metacarpophalangeal joints