Extensor Pollicis Longus

Author: Dr Peter de Souza
Last modified: 13 December 2020

Extensor Pollicis Longus

The structure indicated is the extensor pollicis longus muscle of the posterior forearm.

The extensor pollicis longus muscle is one of the muscles located in the deep layer of muscles in the posterior compartment of the forearm. There are 5 muscles in the deep layer of the posterior forearm:

  1. Supinator
  2. Abductor pollicis longus
  3. Extensor pollicis brevis
  4. Extensor pollicis longus
  5. Extensor indicis

The tendon of the extensor pollicis longus forms the medial border of the anatomical snuffbox. The anatomical snuff box is an anatomical triangle located on the dorsal surface of the hand, it consists of the following boundaries:

  • Medial: Tendon of extensor pollicis longus
  • Lateral: Tendons of extensor pollics brevis and abductor pollics longus
  • Proximal: styloid process of radius
  • Floor: Scaphoid bone and trapezium

A fall onto and outstretched hand often results in fracture of the scaphoid bone. Tenderness in the anatomical snuffbox after a fall onto an outstretched hand is often indicative of a scaphoid fracture.

Origin: Posterior surface of middle third of ulna and interosseous membrane

Insertion: Base of distal phalanx of thumb

Innervation: Posterior interosseous nerve

Action: Extends distal phalanx of thumb at carpometacarpal and interphalangeal joints. Weak extensor of wrist.

Learn more about the muscles of the forearm in this tutorial.