Abductor Pollicis Brevis (Left) (Musculus abductor pollicis brevis)
Educational content only — not medical advice.
Anatomy
The largest and most radial of the thenar muscles, lying superficial to the opponens pollicis. It draws the thumb straight up out of the palm plane and rotates it slightly into a position where the pulp faces the fingers — the opening movement of every pinch. It is the classic muscle for clinical assessment of median motor function.
Origin & insertion
From the tubercle of the scaphoid, the trapezium and the flexor retinaculum, to the radial side of the base of the proximal phalanx of the thumb and its extensor hood.
Action
Abducts the thumb at the carpometacarpal and metacarpophalangeal joints.
Innervation
Recurrent motor branch of the median nerve (C8–T1).
Clinical notes
Isolated APB weakness is the earliest clinical sign of carpal tunnel syndrome, and grading it is the reference test of median motor conduction. Advanced disease hollows the thenar eminence while sensation of the little finger stays intact — the pattern that separates median from ulnar neuropathy.
Related structures
Educational references
FAQ
What is the role of the Abductor Pollicis Brevis (Left)?
The largest and most radial of the thenar muscles, lying superficial to the opponens pollicis. It draws the thumb straight up out of the palm plane and rotates it slightly into a position where the pulp faces the fingers — the opening movement of every pinch. It is the classic muscle for clinical assessment of median motor function.
Why is the Abductor Pollicis Brevis (Left) clinically important?
Isolated APB weakness is the earliest clinical sign of carpal tunnel syndrome, and grading it is the reference test of median motor conduction. Advanced disease hollows the thenar eminence while sensation of the little finger stays intact — the pattern that separates median from ulnar neuropathy.
Source & license
BodyParts3D, © The Database Center for Life Science licensed under CC Attribution 4.0 International (https://creativecommons.org/licenses/by/4.0/). license details