Superficial head of flexor pollicis brevis

At a glance

English

Superficial head of flexor pollicis brevis

Latin (TA2)

Caput superficiale flexoris brevis pollicis

System

Muscle

Region

Upper limb

Side

Paired, left and right

About the superficial head of flexor pollicis brevis

Flexor pollicis brevis is one of the three thenar muscles that form the pad at the base of the thumb. It has two heads. The superficial head is the larger and more constant one; it lies on the ulnar side of abductor pollicis brevis and partly covers opponens pollicis. The deep head is small and lies further in, near the oblique head of adductor pollicis.

The superficial head arises from the flexor retinaculum and from the tubercle of the trapezium. Its fibres run down and laterally along the inner edge of the thenar eminence, beside the tendon of flexor pollicis longus, which passes between the two heads. It ends by a tendon containing the radial sesamoid bone of the thumb and attaches to the proximal phalanx base on its radial side. The deep head, arising from the trapezoid and capitate, joins it there.

The muscle bends the thumb at its metacarpophalangeal joint and helps flex the first metacarpal at the carpometacarpal joint. In this way it assists opposition, bringing the thumb across the palm towards the fingers, and it adds force when the thumb presses an object against the fingertips. The superficial head is usually supplied by the recurrent branch from the median nerve, while the deep head often takes a twig from the ulnar nerve. Its blood comes from the superficial palmar branch of the radial artery.

Because of this split supply, some thumb flexion can survive damage to either nerve alone, which can make the diagnosis of a nerve lesion harder. In carpal tunnel syndrome the superficial head wastes with the other thenar muscles, flattening the thumb pad.

Attachments, action and supply

Origin

Flexor retinaculum and the trapezium tubercle.

Insertion

Thumb proximal phalanx, radial edge of its base, through the radial sesamoid bone.

Action

Bends the thumb knuckle joint and helps flex the first metacarpal, assisting opposition.

Nerve supply

Median nerve, recurrent branch (C8, T1).

Blood supply

Superficial palmar branch of the radial artery.