Extensor pollicis brevis

At a glance

English

Extensor pollicis brevis

Latin (TA2)

Extensor brevis pollicis

System

Muscle

Region

Upper limb

Side

Paired, left and right

About the extensor pollicis brevis

Extensor pollicis brevis is one of the three outcropping muscles of the thumb, which emerge from the deep posterior forearm between the wrist extensors and the finger extensors. It runs alongside, and partly behind, abductor pollicis longus for most of its course.

It arises from the back of the radius below the origin of abductor pollicis longus and from the interosseous membrane next to it. The belly winds obliquely across the lower radius, crossing over the tendons of the two radial wrist extensors. Its tendon then shares the first dorsal compartment under the extensor retinaculum with the abductor tendon, passes over the radial side of the wrist and attaches to the dorsal base of the proximal phalanx of the thumb.

The muscle extends the thumb at the metacarpophalangeal joint, and it also extends and draws back the thumb metacarpal at the carpometacarpal joint. It gives a little help in abducting the hand at the wrist. It is innervated by the posterior interosseous nerve and receives blood from the posterior interosseous artery.

With the thumb stretched out, its tendon forms the front or lateral edge of the anatomical snuffbox, alongside the abductor tendon, while extensor pollicis longus forms the back edge. The radial artery and the scaphoid lie in the floor of this hollow. Inflammation of the shared first compartment, known as de Quervain tenosynovitis, gives pain over the radial styloid that is made worse by bending the thumb into the palm and tilting the wrist towards the ulna.

Attachments, action and supply

Origin

Posterior surface of the radius below abductor pollicis longus, and the adjacent interosseous membrane.

Insertion

Dorsal surface of the base of the proximal phalanx of the thumb.

Action

Extends the thumb at the metacarpophalangeal and carpometacarpal joints; assists abduction of the hand.

Nerve supply

Posterior interosseous nerve (C7, C8).

Blood supply

Posterior interosseous artery.