FPL is the only flexor of the thumb interphalangeal joint. Its AIN innervation makes it the muscle most commonly tested in AIN palsy, inability to flex the thumb IP joint with a normal pinch posture (Kiloh-Nevin sign) indicates AIN pathology.
An expanded entry for Flexor Pollicis Longus.
| Origin | Anterior surface of the radius, middle half, and the adjacent interosseous membrane |
|---|---|
| Insertion | Base of the distal phalanx of the thumb |
| Nerve Supply | Anterior interosseous nerve (AIN, C7, C8, T1) |
| Blood Supply | Anterior interosseous artery |
| Actions |
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|---|
It flexes the tip of the thumb, essential for pinch grip and writing.
AIN palsy (from nerve compression at the pronator teres or spontaneous in Parsonage-Turner syndrome) selectively weakens FPL and FDP to the index, producing the Kiloh-Nevin sign (inability to make an O with the thumb and index, the OK sign). FPL tendon rupture in rheumatoid arthritis occurs from attritional rupture over the scaphoid (Mannerfelt-Norman lesion).
Tested by resisted thumb IP joint flexion with the MCP held extended.
Attritional FPL rupture from scaphoid osteophyte erosion in rheumatoid arthritis (Mannerfelt-Norman lesion) producing sudden loss of thumb tip flexion, requiring tendon graft or FDP transfer.
Other versions of this entry: Flexor Pollicis Longus · Flexor Pollicis Longus (Full)
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