Abductor pollicis brevis muscle
The muscles of thenar are a group comprised of four muscles; abductor pollicis brevis, adductor pollicis, flexor pollicis brevis, and opponens pollicis. They form an elevation located on the radial (lateral) aspect of the palm, named the thenar eminence.
Abductor pollicis brevis is the most lateral and the most superficial of thenar muscles, located underneath the skin. It runs from the scaphoid and trapezium bones, and from the flexor retinaculum to the proximal phalanx of thumb.
In this article, we will discuss the anatomy and function of the abductor pollicis brevis muscle.
|Origin||Tubercles of scaphoid and trapezium bones, Flexor retinaculum|
|Insertion||Lateral aspect of base of proximal phalanx 1 (via radial sesamoid bone)|
|Action||Carpometacarpal joint 1: Thumb abduction|
|Innervation||Recurrent branch of median nerve (C8, T1)|
|Blood supply||Superficial palmar branch of radial artery|
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.
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.
Abductor pollicis brevis is innervated by the recurrent (thenar) branch of median nerve (root value C8 and T1).
Abductor pollicis brevis is vascularized by the superficial palmar branch that arises from the radial artery.
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).