Abductor pollicis longus

At a glance

English

Abductor pollicis longus

Latin (TA2)

Abductor longus pollicis

System

Muscle

Region

Upper limb

Side

Paired, left and right

About the abductor pollicis longus

Abductor pollicis longus belongs to the deep layer of the extensor (posterior) compartment of the forearm. It lies just below supinator, sometimes fused with it, and is the uppermost of the three long muscles that run to the thumb on the back of the forearm; extensor pollicis brevis and extensor pollicis longus lie beneath it in that order.

The muscle arises from the back of the ulna below the anconeus attachment, from the interosseous membrane between the two forearm bones and from the back of the radius in its middle third. Its belly runs downward and outward, emerges between extensor digitorum and extensor carpi radialis brevis, and crosses over the tendons of the radial wrist extensors in the lower forearm. Its tendon then passes, together with that of extensor pollicis brevis, through the first compartment under the extensor retinaculum, in a groove on the outside of the lower radius. It attaches mainly to the first metacarpal, on the radial side of its base, with frequent extra slips to the trapezium, the capsule of the joint and the short thenar muscles. Split tendons are common, and several separate slips may be found.

Its main job is abduction of the thumb at its carpometacarpal joint, carrying it forward and outward from the palm, and it helps to extend and rotate the thumb. Because the tendon crosses the wrist, it also helps to bend the wrist towards the radial side and to flex it. Its pull on the trapezium helps to steady that bone as the thumb grips. Its nerve is the posterior interosseous nerve (C7, C8), which continues the radial nerve's deep branch beyond supinator, and its blood comes from the posterior interosseous artery.

Its tendon forms the front (radial) border of the anatomical snuffbox, the hollow seen at the base of the thumb when it is extended. Inflammation of the shared tendon sheath of this muscle and extensor pollicis brevis causes de Quervain tenosynovitis, painful swelling over the radial styloid, made worse by gripping with the thumb tucked into the fist.

Attachments, action and supply

Origin

Posterior surfaces of the ulna and radius (middle third) and the interosseous membrane between them.

Insertion

First metacarpal, at the radial side of its base, with frequent slips to the trapezium.

Action

Abducts and helps extend the thumb at its carpometacarpal joint; assists radial deviation and flexion of the wrist.

Nerve supply

Posterior interosseous nerve, continuing the radial nerve's deep branch (C7, C8).

Blood supply

Posterior interosseous artery.