Upper limb

First Palmar Interosseous

Musculus interosseus palmaris I

Origin

Ulnar side of the 2nd metacarpal bone

Insertion

Ulnar side of the base of the proximal phalanx of the index finger, with extension into the extensor hood

Function

Adduction of the index finger toward the middle finger axis

Innervation

Ulnar nerve, deep (motor) branch

Movement & chain

Together with the other palmar interossei (PAD: Palmar ADduct), pulls the fingers toward each other, for example when holding a sheet of paper between extended fingers.

Palpation

Deep along the ulnar aspect of the 2nd metacarpal; cannot be palpated separately from intrinsic hand bulk.

Clinical

Adducts the index finger toward the middle finger; tested in suspected ulnar nerve injury (Froment's paper grip test).

Segmental innervation

Ulnar nerve, C8-T1.

In clinical practice

Tested functionally together with adductor pollicis when assessing lateral pinch grip between thumb and index finger in hand rehabilitation.

Region in the model

Upper limb