Extensor Pollicis Longus

Joe Muscolino

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The extensor pollicis longus is seen. The extensor pollicis brevis has been ghosted in.

The Extensor Pollicis Longus is in the Deep Layer of the Posterior Compartment of the forearm. It is also a member of the Deep Distal Four Group; the deep distal four group is composed of:



  • Posterior ulna to the thumb.
    • The proximal attachment is onto the middle 1/3 of the posterior ulna and interosseus membrane.
    • The distal attachment is via its dorsal digital expansion onto the base of the distal phalanx of the thumb.



  • Extends the thumb at the carpometacarpal, metacarpophalangeal, and interphalangeal joints.
  • Laterally rotates the thumb at the carpometacarpal joint.
  • Extends and radially deviates the hand at the wrist joint.
  • Supinates the forearm at the radioulnar joints.



  1. The belly of the extensor pollicis longus lies deep in the posterior forearm, but its distal tendon become superficial farther distally.
  2. The distal tendon of the extensor pollicis longus forms the dorsal digital expansion of the thumb.
  3. The distal tendon of the abductor pollicis longus forms the medial border of the anatomic snuffbox.