APB is the most superficial thenar muscle and the primary palmar thumb abductor. Its unique insertion onto the extensor expansion assists IP extension during opposition.
An expanded entry for Abductor Pollicis Brevis.
| Origin | Flexor retinaculum, scaphoid tubercle, and trapezium |
|---|---|
| Insertion | Radial base of thumb proximal phalanx and lateral extensor expansion |
| Nerve Supply | Recurrent (thenar) branch of median nerve (C8, T1) |
| Blood Supply | Superficial palmar branch of radial artery |
| Actions |
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|---|
It abducts the thumb away from the palm and contributes to opposition, used when grasping a cup or large object.
APB denervation is pathognomonic for median nerve compression at the carpal tunnel. The CMAP amplitude from APB is the electrodiagnostic gold standard for CTS severity. Weakness produces inability to hold the thumb perpendicular to the palm against resistance.
Palpable as the superficial radial thenar bulk beneath the thumb MCP joint during palmar abduction.
Reduced APB CMAP amplitude indicating axonal loss, requiring urgent surgical decompression.
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