Extensor Pollicis Longus

Origin

The extensor pollicis longus muscle originates from the:

- posterior surface of middle one third of the body of ulna, which is located inferior to the origin site of the abductor pollicis longus muscle;

- adjacent interosseous membrane of forearm.

Insertion

The fibers of the extensor pollicis longus muscle travel inferolaterally to the hand and insert, via a long tendon, onto the dorsal aspect of the base of the distal phalanx of thumb.

Key Features & Anatomical Relations

The extensor pollicis longus is one of the muscles of the deep part of the posterior compartment of the forearm. It is a long, fusiform type of skeletal muscle.

Superior to the wrist, the muscle belly gives rise to a tendon which travels inferolaterally, towards the medial aspect of the dorsal radial tubercle. The tendon hooks around the tubercle to change its line of pull in a more lateral direction. At the wrist, its tendon travels deep to the extensor retinaculum of hand, where it passes through the tendinous sheath of extensor pollicis longus. Within the hand, the tendon then travels inferolaterally to its insertion site.

The extensor pollicis longus muscle is located:

- anterior (deep) to the extensor digitorum and extensor digiti minimi muscles and the posterior interosseous artery;

- posterior (superficial) to the body of the radius and adjacent interosseous membrane of the forearm (at its muscle belly), and the tendons of the extensor carpi radialis longus and brevis muscles (at its tendon);

- medial to the extensor pollicis brevis and abductor pollicis longus muscles;

- lateral to the extensor indicis muscle.

The tendon of the extensor pollicis longus forms the posterior boundary of the anatomical snuff box, while the tendons of both the extensor pollicis brevis and abductor pollicis longus form its anterior boundary.

Actions & Testing

The extensor pollicis longus muscle is involved in multiple actions:

- extends the distal phalanx of thumb at its interphalangeal joint;

- extends the proximal phalanx of thumb at the first metacarpophalangeal joint;

- extends the first metacarpal bone (of thumb) at the first carpometacarpal joint;

- assists in extension of the hand at the radiocarpal (wrist) joint.

The extensor pollicis longus muscle can be tested by extending the distal phalanx of thumb at its interphalangeal joint against resistance. It can be seen and palpated along the posterior boundary of the anatomical snuff box (Standring, 2016).

List of Clinical Correlates

- Hammer thumb

References

Standring, S. (2016) Gray's Anatomy: The Anatomical Basis of Clinical Practice. Gray's Anatomy Series 41st edn.: Elsevier Limited.