Abductor pollicis brevis muscle

Origin and insertion

Abductor pollicis brevis originates from several locations. The majority of muscle fibers originate from the broadest origin area located on flexor retinaculum. Two smaller origins are located on carpal bones; the first is found on the tubercle of scaphoid while the second is on the tubercle of trapezium bone.

After originating from these locations, the muscle fibers form a single muscle belly that runs distally and radially (lateral) towards the thumb. Near the insertion, the muscle ends in a flat tendon that inserts onto the radial aspect of the base of the proximal phalanx of thumb. Lateral slips of the tendon join the expansion of extensor pollicis longus tendon.

Relations

Abductor pollicis brevis is a fusiform muscle located at the surface of the thenar eminence, directly superior to opponens pollicis and flexor pollicis brevis muscles. These three muscles comprise a gap through which the thenar branch of median nerve passes. The superficial palmar branch of radial artery runs across the superficial aspect of abductor pollicis brevis.

Innervation

Abductor pollicis brevis is innervated by the recurrent (thenar) branch of median nerve (root value C8 and T1).

Blood supply

Abductor pollicis brevis is vascularized by the superficial palmar branch that arises from the radial artery.

Function

The main action of abductor pollicis brevis muscle is the abduction of thumb at the carpometacarpal and metacarpophalangeal joints. This action happens in synergy with abductor pollicis longus muscle. Abductor pollicis brevis also facilitates the movement of the thumb towards the fingertips in the carpometacarpal joint (opposition) and flexion in the metacarpophalangeal joint. All of the aforementioned functions of this muscle are of great significance for the proper functioning of the hand, such as grasping round objects or carrying out tasks that demand precision (e.g. writing and sewing).

Test your knowledge on the muscles of the hand with this quiz.