abductor pollicis brevis muscle

The abductor pollicis brevis (abductor brevis) is a muscle in the hand that abducts the thumb, moving it away from the plane of the palm. It forms the bulk of the thenar eminence on the radial (thumb) side of the palm.

The abductor pollicis brevis lies superficially on the radial side of the palm, forming the most prominent visible part of the thenar eminence. It originates from the flexor retinaculum and scaphoid and trapezium bones and inserts into the lateral side of the base of the proximal phalanx of the thumb.

The primary function of the abductor pollicis brevis is to abduct the thumb — pulling it away from the index finger and forward away from the palm (palmar abduction). This movement is the first step in the opposition of the thumb to the other fingers.

This muscle is innervated by the recurrent branch of the median nerve, so carpal tunnel syndrome (median nerve compression at the wrist) can weaken or paralyze it. Thenar muscle wasting with loss of abductor pollicis brevis function is a classic sign of advanced carpal tunnel syndrome.

The abductor pollicis brevis is a short intrinsic hand muscle forming the thenar eminence, while the abductor pollicis longus is a longer extrinsic muscle originating in the forearm. The brevis produces finer, more precise palmar abduction, whereas the longus provides more powerful radial abduction and wrist movement.