The abductor pollicis longus is one of the three muscles of the posterior forearm that act on the thumb, its tendon passing through the first extensor compartment at the wrist alongside the extensor pollicis brevis. These two tendons form the anterior boundary of the anatomical snuffbox and the lateral boundary of the thumb in de Quervain tenosynovitis, the most common tendon entrapment syndrome of the wrist.
| Origin | Posterior surface of the interosseous membrane, posterior radius, and posterior ulna |
|---|---|
| Insertion | Lateral aspect of the base of the first metacarpal |
| Nerve Supply | Posterior interosseous nerve (C7, C8) |
| Blood Supply | Posterior interosseous artery |
| Actions |
|
|---|
It abducts and extends the first metacarpal, positioning the thumb away from the palm to allow grasp. The distinction between its abduction action (in the plane of the palm) and the extensor pollicis brevis extension action (perpendicular to the palm) is important for understanding de Quervain anatomy.
De Quervain tenosynovitis involves stenosing inflammation of the first extensor compartment tendon sheath containing the APL and EPB tendons, producing radial wrist pain reproduced by the Finkelstein test. The APL often has multiple tendon slips, a common anatomical variant that increases the chance of incomplete decompression if not identified at surgery. De Quervain is strongly associated with new parenthood from repetitive infant lifting.
The APL tendon is palpable as the more anterior and thicker of the two tendons forming the anterior boundary of the anatomical snuffbox, becoming prominent during thumb abduction in the plane of the palm.
Stenosing tenosynovitis of the first extensor compartment containing the APL and EPB tendons producing radial wrist pain reproduced by the Finkelstein test, managed with splinting, injection, and surgical decompression for refractory cases.
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