Extensor Pollicis Brevis Muscle Anatomy

The belly of the extensor pollicis brevis (EPB), the fusiform short extensor of the thumb, lies distal to the abductor pollicis longus and is partly covered by it. Its tendon lies parallel and immediately medial to that of the APL but extends farther, reaching the base of the proximal phalanx.

Extensor Pollicis Brevis Muscle Anatomy

The extensor pollicis brevis muscle originates from the lower third of the posterior surface of the radius and the interosseous membrane. It inserts on the base of the proximal phalanx of the thumb.

It’s innervated by the supplied by the posterior interosseous nerve (C7 & C8). The blood supply to this musclr comes from supplied by the posterior interosseous artery, which originates from the common interosseous branch of the ulnar artery.

In continued action after acting to flex the proximal phalanx of the thumb, or acting when that joint is fixed by its antagonists, it helps extend the 1st metacarpal and extend and abduct the hand. When the thumb is fully extended, a hollow, called the anatomical snuff box, can be seen on the radial aspect of the wrist.

See Also: Forearm Muscles Anatomy & Function

Anatomical snuff box: When the thumb is extended, a triangular hollow appears between the tendon of the extensor pollicis longus (EPL) medially and the tendons of the extensor pollicis brevis (EPB) and abductor pollicis longus (APL) laterally. The floor of the snuff box, formed by the scaphoid and trapezium bones, is crossed by the radial artery as it passes diagonally from the anterior surface of the radius to the dorsal surface of the hand.

See Also: Wrist & Hand Examination

Inflammation can occur in the tendons of the extensor pollicis brevis and the abductor pollicis longus, the so called De Quervain’s Tenosynovitis. This condition can be assessed by Finkelstein Test.

To test the extensor pollicis brevis, the thumb is extended against resistance at the metacarpophalangeal joint. If the extensor pollicis brevis is acting normally, the tendon of the muscle can be seen and palpated at the lateral side of the anatomical snuff box and on the medial side of the adjacent abductor pollicis longus tendon.

References & More

1. Cael, C. (2010). Functional anatomy: Musculoskeletal anatomy, kinesiology, and palpation for manual therapists. Philadelphia, PA: Wolters Kluwer Health/Lippincott, Williams & Wilkins.
2. Moore, K. L., Dalley, A. F., & Agur, A. M. R. (2014). Clinically Oriented Anatomy (7th ed.). Philadelphia, PA: Lippincott Williams & Wilkins.
3. Clinically Oriented Anatomy – 8th Edition
4. Jabir S, Lyall H, Iwuagwu FC. The extensor pollicis brevis: a review of its anatomy and variations. Eplasty. 2013 Jul 1;13:e35. PMID: 23882301; PMCID: PMC3701420. Pubmed