Abductor pollicis brevis abducts the thumb at the carpometacarpal and MCP joints.
The abductor pollicis brevis (APB) is a superficial intrinsic muscle of the hand and a key component of the thenar eminence. It is primarily responsible for abducting the thumb at the carpometacarpal and metacarpophalangeal joints, playing a crucial role in thumb opposition, grip, and fine motor function.
The APB is located on the lateral aspect of the palm, forming the most superficial and lateral part of the thenar eminence. It lies superficial to the flexor pollicis brevis and lateral to the opponens pollicis.
This short, flat, triangular muscle spans from the flexor retinaculum and carpal bones to the proximal phalanx of the thumb.
The abductor pollicis brevis serves multiple functional roles:
The muscle is innervated by the recurrent branch of the median nerve (C8–T1).
The APB lies superficial and lateral within the thenar eminence. It is bordered medially by the flexor pollicis brevis and deeper structures like the opponens pollicis. The palmar cutaneous branch of the median nerve lies superficial to it.
The abductor pollicis brevis forms the most prominent surface bulge of the thenar eminence and becomes especially visible during active thumb abduction. It can be palpated just lateral to the base of the thumb.
The APB originates from mesenchymal condensations of the thenar muscle mass during embryonic hand development. Its innervation by the median nerve reflects its anterior (preaxial) compartment origin.
In non-human primates, the abductor pollicis brevis is less developed or absent, reflecting limited thumb mobility. In humans, its specialization allows for fine thumb movements that enable tool use, writing, and intricate manual tasks.