Extensor pollicis brevis

A forearm muscle whose tendon runs through the first extensor compartment, beside the abductor pollicis longus, to the base of the thumb's proximal phalanx; it straightens the thumb's knuckle joint. It often lies in its own sub-compartment, which a steroid injection may miss and which must be found and opened at surgery for De Quervain's tenosynovitis.

Related terms

• Anatomy

  First extensor compartment

  The fibro-osseous tunnel over the radial styloid through which the abductor pollicis longus and extensor pollicis brevis tendons pass under the extensor retinaculum. A septum divides it fully or partly in many wrists, more often in people with De Quervain's tenosynovitis, and the abductor pollicis longus often has several slips — both relevant to injection and to surgical release.

• Anatomy

  Abductor pollicis longus

  A forearm muscle whose tendon passes through the first extensor compartment and inserts on the base of the thumb metacarpal; it moves the thumb away from the palm and steadies the thumb base. Its tendon usually has two or more slips, which can hide a separate compartment during surgery for De Quervain's tenosynovitis.

Articles mentioning this term

1. Patient information · 2 October 2026

   De Quervain's tenosynovitis

   Pain on the thumb side of the wrist: how De Quervain's tenosynovitis is diagnosed, what splints and steroid injections do, and what surgery involves.

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