Extensor Pollicis Brevis

Origin

The extensor pollicis brevis muscle originates from the:

- posterior surface of distal half of the body of the radius, 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 brevis muscle travel inferolaterally to the hand and insert, via a thin tendon, onto the dorsal aspect of the base of the proximal phalanx of thumb.

Key Features & Anatomical Relations

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

Superior to the wrist, the muscle belly gives rise to a tendon which travels inferolaterally, spiraling over the distal radius and the tendons of the brachioradialis and extensor pollicis longus and brevis muscles. At the wrist, its tendon travels deep to the extensor retinaculum of hand, along with the adjacent tendon of abductor pollicis longus, where it passes through the common tendinous sheath of abductor pollicis longus and extensor pollicis brevis muscles. Within the hand, the tendon then travels inferolaterally to its insertion site.

The extensor pollicis brevis muscle is located:

- anterior (deep) to the extensor digitorum and extensor pollicis longus muscles;

- posterior (superficial) to the body of radius and adjacent interosseous membrane of forearm;

- medial to the abductor pollicis longus muscle;

- lateral to the extensor pollicis longus muscle.

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

Actions & Testing

The extensor pollicis brevis muscle is involved in multiple actions:

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

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

The extensor pollicis brevis muscle can be tested by extending the proximal phalanx of thumb at the first metacarpophalangeal joint against resistance. It can be seen and palpated along the anterior boundary of the anatomical snuff box (Standring, 2016).

List of Clinical Correlates

- de Quervain disease

References

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