APL typically has multiple tendon slips (1-4) inserting on the first metacarpal base, contributing to de Quervain stenosing tenosynovitis alongside EPB in the first extensor compartment.
| Origin | Posterior radius, ulna and interosseous membrane — distal half |
|---|---|
| Insertion | Base of the first metacarpal — lateral aspect |
| Nerve Supply | Posterior interosseous nerve (C7, C8) |
| Blood Supply | Posterior interosseous artery |
| Actions | Abducts the thumb at the CMC joint; Assists thumb extension and wrist radial deviation |
|---|
Multiple APL slips may occupy separate sub-compartments within the first compartment, requiring individual release for complete decompression. The Finkelstein test stretches APL and EPB.
Palpable at the base of the anatomical snuffbox during thumb abduction.
Stenosing tenosynovitis of APL in the first extensor compartment, treated by ultrasound-guided steroid injection or surgical release.
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