Abductor Pollicis Longus

The abductor pollicis longus 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 proximal ulna and radial shafts
  • Adjacent interosseus membrane
Insertion

It usual splits into 2 slips distally:

  • radial side – first metacarpal base
  • trapezium

The abductor pollicis longus emerges distally between the extensor digitorum and the extensor carpi radialis brevis muscles to form its tendon which runs in a groove within the lateral side of the distal radius, accompanied by the tendon of the extensor pollicis brevis.

Innervation
  • Posterior interosseus nerve
Blood Supply
  • Proximal – branch of posterior interosseus artery
  • Distal – branch of anterior interosseus artery
Action
  • Abduction of the wrist
  • Abduction and extension of the thumb