Abductor pollicis brevis

At a glance

English

Abductor pollicis brevis

Latin (TA2)

Abductor brevis pollicis

System

Muscle

Region

Upper limb

Side

Paired, left and right

About the abductor pollicis brevis

The thenar eminence, the rounded pad at the base of the thumb, contains three short muscles. Abductor pollicis brevis is the most superficial and lateral of them, lying just under the skin and fascia, with flexor pollicis brevis on its inner side and opponens pollicis beneath it. Because it lies so close to the surface, it can easily be felt and seen contracting.

It arises from the front of the flexor retinaculum and from the tubercles of the scaphoid and trapezium bones of the wrist. Often it receives a slip from the tendon of abductor pollicis longus too. The fibres run downward and outward to a thin tendon that attaches to the base of the thumb's proximal phalanx on its radial side and to the metacarpophalangeal joint capsule, with some fibres joining the extensor expansion on the back of the thumb.

In the hand, abduction of the thumb means moving it forward, at right angles to the palm, rather than sideways. Abductor pollicis brevis produces this movement at the carpometacarpal and metacarpophalangeal joints, as when the thumb is moved forward to grip a large cup. It also helps to bring the thumb into opposition with the fingers and, through the extensor expansion, assists in straightening the thumb joints. It is supplied by the recurrent (thenar) branch of the median nerve, which carries fibres from the eighth cervical and first thoracic segments, and receives blood from the superficial palmar branch of the radial artery.

The muscle is the standard one for testing the median nerve. In carpal tunnel syndrome the nerve is squeezed under the flexor retinaculum, and weakness and wasting of abductor pollicis brevis flatten the thenar eminence. Examiners test it by asking the patient to raise the thumb towards the ceiling, with the hand palm-up, against resistance. The recurrent branch lies just under the skin over the thenar muscles and can be cut by small wounds there.

Attachments, action and supply

Origin

Flexor retinaculum and the tubercles of the scaphoid and trapezium.

Insertion

Base of the thumb's proximal phalanx (radial side) and the metacarpophalangeal joint capsule.

Action

Abducts the thumb at the carpometacarpal and metacarpophalangeal joints; assists thumb opposition and extension.

Nerve supply

Median nerve, recurrent (thenar) branch (C8, T1).

Blood supply

Superficial palmar branch of the radial artery.