Extensor Pollicis Brevis

Original Editor - Oyemi Sillo

Top Contributors - Oyemi Sillo

Description

The extensor pollicis brevis (EPB) belongs to the deep group of the posterior fascial compartment of the forearm.[1] It is a part of the lateral border of the anatomical snuffbox.[2]

Origin

The extensor pollicis brevis originates from the lower third of the posterior surface of the radius and the interosseous membrane.[2]

Insertion

It inserts on the base of the proximal phalanx of the thumb.[2]

Nerve

The EPB is supplied by the posterior interosseous nerve (C7 & C8), the continuation of the deep branch of the radial nerve.[2]

Artery

The EPB is supplied by the posterior interosseous artery, which originates from the common interosseous branch of the ulnar artery.[2]

Function

This muscle extends the thumb at the metacarpophalangeal and carpometacarpal joints.[2] It is also a mild abductor of the thumb.[3]

Clinical relevance

The tendons of the EPB and the Abductor Pollicis Longus (APL) are enclosed in a common sheath at the dorsum of the wrist. Forceful or repetitive movements of the thumb and wrist can increase the friction between both tendons, causing inflammation in their shared tendon. This condition, known as De Quervain's Tenosynovitis, causes pain in the radial aspect of the wrist that radiates to the proximal part of the forearm.[4]

Assessment

De Quervain's Tenosynovitis can be assessed with a test called Finkelstein Test: the examiner grasps the patient's thumb with one hand and holds the patient's forearm in neutral position with the other hand. The examiner then pulls on the patient's thumb longitudinally with a slight ulnar deviation at the wrist. Increased pain at the radial styloid process indicates a positive test.[5]

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Treatment

Physiotherapy treatment for De Quervain's Tenosynovitis involves:[6]

  • Immobilization of the thumb and wrists with splints, to give the tendons time to heal.
  • Myofascial release, soft-tissue massage and ice packs, to reduce pain.
  • Muscle strengthening and stretching, to improve mobility.
  • Ergonomic education, joint protection techniques


Medical and surgical treatments include:

  • NSAIDs
  • Corticosteroid injections
  • Surgical release of the tendon sheath

Resources

References

  1. Snell R. Clinical Anatomy by Regions. Philadelphia: Lippincott Williams & Wilkins, 2008 
  2. 2.0 2.1 2.2 2.3 2.4 2.5 Drake R, Vogl W, Mitchell A. Gray's Anatomy for Students E-Book. Philadelphia: Elsevier Health Sciences, 2009.
  3. Smutz WP, Kongsayreepong A, Hughes RE, Niebur G, Cooney WP, An KN. Mechanical advantage of the thumb muscles. J Biomech. 1998 Jun;31(6):565-70.
  4. Agur A, Dalley A. Grant's atlas of anatomy. Philadelphia: Lippincott Williams & Wilkins, 2009
  5. Goubau J, Goubau L, Tongel A, Hoonacker P, Kerckhove D & Berghs B. The wrist hyperflexion and abduction of the thumb (WHAT) test: a more specific and sensitive test to diagnose de Quervain tenosynovitis than the Eichhoff's test. The Journal of hand surgery. 2013. European volume. 39. 10.1177/1753193412475043.
  6. Brigham and Women's Hospital. Standard of Care: de Quervain’s Syndrome: Nonoperative Management. 2007 [1]