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