Oblique head of adductor pollicis

At a glance

English

Oblique head of adductor pollicis

Latin (TA2)

Caput obliquum adductoris pollicis

System

Muscle

Region

Upper limb

Side

Paired, left and right

About the oblique head of adductor pollicis

Adductor pollicis is a triangular, fanned muscle lying deep within the palm that pulls the thumb towards the hand. It has two heads: an oblique head above, arising near the wrist, and a transverse head below, arising from the third metacarpal. The two meet at the thumb and act as one.

The oblique head arises from the capitate, from the index and middle metacarpal bases, from the palmar carpal ligaments, and from the sheath around the tendon of flexor carpi radialis. Its fibres run obliquely across the palm towards the thumb, beneath the lumbricals and the long finger flexor tendons. Near the thumb they join the transverse head in a common tendon, which contains a sesamoid bone and attaches to the thumb proximal phalanx, on the ulnar edge of its base. Some fibres pass on to the extensor expansion.

The muscle draws the thumb towards the palm and the index, closing the gap between them. It is essential for a strong key or pinch grip and for holding objects against the side of the index. With the thumb opposed, it adds force to grasping. The ulnar nerve supplies it through its deep branch, and its blood comes from the deep palmar arch, which, like the nerve, passes between the two heads.

When the ulnar nerve is injured the muscle weakens. Asked to grip a sheet of paper between thumb and index, the patient bends the thumb tip with flexor pollicis longus to make up for it, a response known as the Froment sign. The thumb ulnar collateral ligament lies just under the insertion, and injury to it is called skier thumb.

Attachments, action and supply

Origin

Capitate, the index and middle metacarpal bases, the nearby palmar carpal ligaments and the flexor carpi radialis tendon sheath.

Insertion

With the transverse head, the ulnar edge of the thumb proximal phalanx base, by way of the ulnar sesamoid bone.

Action

Adducts the thumb towards the palm and index; strengthens pinch and grip.

Nerve supply

Ulnar nerve, deep branch (C8, T1).

Blood supply

Deep palmar arch.