Abductor pollicis longus
Musculus abductor pollicis longus
Also known as: APL
A deep "outcropping" muscle of the posterior forearm that abducts the thumb at the carpometacarpal joint. It forms part of the anterior boundary of the anatomical snuffbox.
Overview
APL arises from the posterior surfaces of the ulna, radius and interosseous membrane below supinator. It emerges between ECRB and extensor digitorum, crosses over the radial wrist extensors, and passes through the 1st extensor compartment with EPB, often as several tendon slips. It inserts on the lateral side of the base of the 1st metacarpal (and often the trapezium). It abducts the thumb at the carpometacarpal joint and extends it there, and it assists radial deviation of the wrist.
Anatomy
- Origin
Posterior surfaces of the ulna, radius and interosseous membrane.
- Insertion
Lateral base of the 1st metacarpal.
- Action
Abduction (and extension) of the thumb at the carpometacarpal joint.
- Innervation
Posterior interosseous nerve.
- Nerve roots
C7–C8
- Arterial supply
Posterior interosseous artery.
Function
- Abducts and extends the thumb at the CMC joint
- Assists radial deviation of the wrist
Clinical significance
De Quervain tenosynovitis
Thickening of the 1st dorsal compartment sheath around APL and EPB causes radial-sided wrist pain made worse by thumb movement (positive Finkelstein test). Treated with a splint, corticosteroid injection or surgical release.
Compiled from standard anatomy and physiology references — see the Muscular System sources. For education only; not medical advice.