The interosseus muscles of the hand, as the name suggests, are found between ("inter") the bones ("osseus") of the hand, specifically the metacarpals. They consist of a dorsal and a palmar set of muscles.

The dorsal interossei are bipennate, the palmar interossei are unipennate

The function of these muscles is to abduct and adduct the digits. The palmar interossei ADduct, the dorsal interossei ABduct. This can be remembered with the mnemonic "PAD and DAB" - Palmar ADduct, Dorsal ABduct.

Origin

The interossei attach to the proxmial phalanx and extensor hood of each finger.

  • Dorsal interossei: bipennate muscles which attach to the sides of metacarpals 1 to 5.
  • Palmar interossei: unipennate muscles which attach to the sides of metacarpals 1 (medial), 2 (medial), 4 (lateral) and 5 (lateral) – the middle finger has no palmar interosseus muscle.
Insertion
  • Dorsal interossei: Base of proximal phalanx and extensor expansion of associated digit. First is largest, inserts into lateral side of index finger, second inserts into lateral side of middle finger, third inserts into medial side of middle finger, fourth inserts into medial side of ring finger
  • Palmar interossei: Base of proximal phalanx and extensor expansion of associated digit.

The first palmar interosseus muscle is often rudimentary due to the other muscles of the thumb involved in adduction – e.g. adductor pollicis. When present, the first palmar interosseus originates from the medial surface of the thumb arpal and inserts into the base of the proximal phalanx and the extensor hood.

Palmar interossei are smaller than dorsal.

The tendons pass deep to the deep transverse metacarpal ligaments.

The thumb and little finger have separate muscles for abduction – abductor digiti minimi and abductor pollicis brevis, therefore do not have dedicated dorsal interossei.

The radial artery passes between the heads of the first doral interosseus muscle.

Innervation
  • Deep Branch of Ulnar Nerve
Blood Supply

Palmar interossei

  • Branches of the deep palmar arch
  • princeps pollicis
  • radialis indicis
  • palmar metacarpal arteries
  • tendons – branches from common and proper digital arteries

Dorsal interossei

  • Dorsal and palmar metacarpal arteries
  • princeps pollicis
  • radialis indicis
  • branches from deep palmar arces
  • tendons – branches from common and proper palmar and dorsal digital arteries
Action

The function of these muscles is to abduct and adduct the digits. The palmar interossei ADduct, the dorsal interossei ABduct. This can be remembered with the mnemonic “PAD and DAB” – Palmar ADduct, Dorsal ABduct.

In addition:

  • Assist flexion (at MCP) and extension (interphalangeal joints) via extensor expansion attachment