Definition

By: Gregory R. Waryasz, MD

The extensor pollicis brevis muscle of the musculoskeletal system is characterized by passing through extensor compartment one along with the abductor pollicis longus.

It is part of the forearm.  It consists of skeletal muscle fibers.

Its unique structural features include its tendon passing with the abductor pollicis longus through the first extensor compartment. The muscle belly is a fusiform shape.  The tendon lies parallel and medial to the abductor pollicis longus.

The origin is the posterior surface of the distal third of the radius and interosseous membrane.

The insertion is the base of the dorsal aspect of the proximal phalanx of the thumb.

The blood supply is from the posterior interosseous artery and venous drainage is from the accompanying veins.

The innervation is from the posterior interosseous nerve.

The extensor pollicis brevis muscle as well as all other bones, muscles, and ligaments of the body are derived of mesodermal origin in the embryo.

The function of the extensor pollicis brevis is to extend the proximal phalanx of the thumb at the metacarpophalangeal joint. It also helps to extend the carpometacarpal joint.  The synergists are the abductor pollicis longus and the extensor pollicis longus.

Common diseases include tendon rupture and tenosynovitis.

Tendon rupture can occur from trauma.

Tenosynovitis of the 1st compartment tendons (extensor pollicis brevis and abductor pollicis longus) is known as de Quervain tenosynovitis.  The tendons become inflammed beneath the retinacular pulley at the radial styloid. There is point tenderness over the 1st compartment.  A Finkelstein test involves ulnar deviation with the thumb enclosed in the palm.

Commonly used diagnostic procedures include clinical history, physical exam and MRI.

It is usually treated with NSAIDs, physical therapy, splinting, and sometimes surgery for de Quervain tenosynovitis.  Tendon rupture may require surgery to reconstruct the tendon.

References

Lieberman J (ed), AAOS Comprehensive Orthopaedic Review, American Academy of Orthopaedic Surgeons, 2008.

Moore K, Dalley A (eds), Clinically Oriented Anatomy (5th edition), Lippincott Williams & Wilkins, Philadelphia, PA, 2006.

Wheeless’ Textbook of Orthopaedics: Extensor Pollicis Brevis (http://www.wheelessonline.com/ortho/extensor_pollicis_brevis)