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.

Related terms

• Condition

  De Quervain's tenosynovitis

  Painful thickening of the first extensor compartment at the wrist, so that the abductor pollicis longus and extensor pollicis brevis tendons no longer glide freely. It causes pain over the thumb side of the wrist on gripping and pinching, is commoner in women, after 40 and around pregnancy, and is treated with a splint, a steroid injection or, if these fail, 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.

• Anatomy

  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.

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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