Upper limb

Adductor Pollicis

Musculus adductor pollicis

Origin

Oblique head: capitate bone and base of the 2nd/3rd metacarpal bones; transverse head: palmar surface of the 3rd metacarpal bone

Insertion

Ulnar side of the base of the proximal phalanx of the thumb, via a sesamoid bone

Function

Adduction of the thumb toward the palm; principal muscle for key pinch grip

Innervation

Ulnar nerve, deep (motor) branch

Movement & chain

The strongest thenar-related muscle for key pinch between the thumb and the side of the index finger, for example when holding a key or a card.

Palpation

Palpable in the first web space between thumb and index finger when squeezing a sheet of paper closed without using the fingertips.

Clinical

Loss of function produces a positive Froment's sign: compensatory flexion of the thumb IP joint by flexor pollicis longus (median nerve) during attempted adduction, indicating ulnar nerve injury.

Segmental innervation

Ulnar nerve, C8-T1.

In clinical practice

The strength of this muscle is used in hand function assessment and dynamometry as a measure of key pinch grip, a sensitive indicator of ulnar nerve function.

Region in the model

Upper limb