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- Posterior radius to the thumb.
- The proximal attachment is onto the distal 1/3 of the posterior radius and interosseus membrane.
- The distal attachment is onto the base of the proximal phalanx of the thumb.
- Extends the thumb at the carpometacarpal and metacarpophalangeal joints.
- Abducts the thumb at the carpometacarpal joint.
- Laterally rotates the thumb at the carpometacarpal joint.
- Radially deviates the hand at the wrist joint.
- The belly of the extensor pollicis brevis lies deep in the posterior forearm, but its distal tendon become superficial farther distally.
- The distal tendons of the abductor pollicis longus and extensor pollicis brevis travel together in a common synovial sheath and form the lateral border of the anatomic snuffbox.
- The distal tendons of abductor pollicis longus and extensor pollicis brevis are involved in deQuervain’s syndrome (deQuervain’s stenosing synovitis).