Adductor pollicis
Musculus adductor pollicis
A deep, fan-shaped two-headed muscle of the palm that adducts the thumb, providing a powerful key-pinch. It is supplied by the ulnar nerve and tested with Froment's sign.
Overview
Adductor pollicis lies deep in the palm, in the adductor compartment, beneath the long flexor tendons and the lumbricals. It has an oblique head, from the capitate and the bases of the 2nd and 3rd metacarpals, and a transverse head, from the anterior shaft of the 3rd metacarpal. The two heads converge on the medial side of the base of the proximal phalanx of the thumb, via the medial sesamoid, and the extensor expansion. The radial artery enters the palm between its two heads to form the deep palmar arch.
It adducts the thumb toward the palm and is essential for key (lateral) pinch and a forceful grip. Although it lies on the thumb side, it is not a thenar muscle. It is supplied by the deep branch of the ulnar nerve, the last muscle that branch supplies.
Parts & subdivisions
- Oblique headCapitate and the bases of the 2nd and 3rd metacarpals.
- Transverse headAnterior shaft of the 3rd metacarpal.
Anatomy
- Origin
Oblique head: capitate and the bases of the 2nd and 3rd metacarpals. Transverse head: anterior surface of the shaft of the 3rd metacarpal.
- Insertion
Medial side of the base of the proximal phalanx of the thumb (via the ulnar sesamoid) and the extensor expansion.
- Action
Adduction of the thumb at the CMC and MCP joints.
- Innervation
Deep branch of the ulnar nerve.
- Nerve roots
C8–T1
- Arterial supply
Deep palmar arch (radial artery).
Function
- Adducts the thumb
- Provides power for key pinch and grip
Clinical significance
Froment's sign
Asked to grip a sheet of paper between the thumb and the side of the index finger, a patient with an ulnar nerve lesion flexes the thumb IP joint. They are substituting FPL (median nerve) for the paralysed adductor pollicis.
Gamekeeper's / skier's thumb
Rupture of the ulnar collateral ligament of the thumb MCP joint. A Stener lesion occurs when the adductor aponeurosis becomes interposed between the torn ligament and its insertion, which prevents healing and needs surgery.
Compiled from standard anatomy and physiology references — see the Muscular System sources. For education only; not medical advice.