Palmar interossei muscles

At a glance

English

Palmar interossei muscles

Latin (TA2)

Musculi interossei palmares

System

Muscle

Region

Upper limb

Side

Paired, left and right

About the palmar interossei muscles

The palmar interossei are a set of slender muscles lying in the spaces between the metacarpal bones, on the palm side of the dorsal interossei. Usually three are counted, one each for the index, the ring and the little finger; some texts add a fourth, a small slip on the thumb that is often merged with neighbouring thenar muscles. The middle finger has none, because it is the line towards which the others are drawn.

Each palmar interosseous has a single head, unlike the two-headed dorsal ones. It springs from the shaft of one metacarpal only, on the side that faces the middle finger: the second metacarpal on its ulnar side, and the fourth and fifth on their radial sides. The muscle passes forward behind the deep transverse metacarpal ligament and ends on the same finger, attaching to the extensor expansion and in part to the side of the proximal phalanx base.

Their main action is adduction of the fingers, bringing the index, the ring and the little finger in towards the middle finger. A common memory aid is PAD for palmar adduct and DAB for dorsal abduct. Through their pull on the extensor expansion they also help the lumbricals bend the knuckles while straightening the finger joints. All of them are innervated in the palm by the deep ulnar branch, and they receive blood from the palmar metacarpal arteries off the deep palmar arch.

Their strength is tested by asking the patient to hold a card between two straight fingers while the examiner tries to pull it out. Weakness points to an ulnar nerve lesion. Wasting of the interossei gives hollows between the metacarpals, seen best on the back of the hand.

Attachments, action and supply

Origin

Shafts of the second, fourth and fifth metacarpals, on the side facing the middle finger.

Insertion

Extensor expansion and side of the proximal phalanx of the same finger.

Action

Adduct the index, ring and fifth fingers towards the middle finger; help flex the knuckles and extend the interphalangeal joints.

Nerve supply

Ulnar nerve, its deep branch (C8, T1).

Blood supply

Palmar metacarpal arteries from the deep palmar arch.