Abductor pollicis brevis forms part of the thenar eminence of the palm.
It arises from the tubercle of the scaphoid and the flexor retinaculum. It may also arise from the tubercle of the trapezium. It is inserted into the radial side of the base of the proximal phalanx and into the tendon of extensor pollicis longus.
It abducts the thumb at both the metacarpophalangeal and carpometacarpal joints. Thumb abduction entails movement in a plane perpendicular to the palm. Also, abductor pollicis brevis contracts during the early stages of opposition of the thumb; during this movement, it also acts to rotate the phalanx. Finally, by virtue of its attachment to the tendon of extensor pollicis longus, it assists in extension of the thumb.
The nerve supply is very variable:
- usually, the recurrent branch of the median nerve (C8, T1)
- infrequently, the deep branch of the ulnar nerve
- infrequently, supply from both nerves