CorpusHuman Anatomy
MuscularMuscle group

Interossei (hand)

Musculi interossei manus

Also known as: dorsal interossei, palmar interossei, interosseous muscles, PAD, DAB

Small muscles between the metacarpals: four dorsal (abductors) and three palmar (adductors). They spread and close the fingers and, like the lumbricals, flex the MCP joints and extend the IP joints.

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Overview

The interossei occupy the spaces between the metacarpals. Movements are described relative to the axis of the middle finger.
- Dorsal interossei (4): bipennate, each arising from the two adjacent metacarpals. They insert into the bases of the proximal phalanges and the extensor expansions of the index finger (lateral side), the middle finger (both sides) and the ring finger (medial side). They abduct the digits away from the middle-finger axis (DAB). The 1st dorsal interosseous forms the bulge of the first web space.
- Palmar interossei (3): unipennate, each from a single metacarpal (2nd, 4th, 5th). They insert on the side of the digit facing the middle finger and adduct the digits toward it (PAD). A small 4th palmar interosseous to the thumb is inconstant.

Through the extensor expansions, both sets also flex the MCP joints and extend the IP joints, assisting the lumbricals. The thumb and little finger have their own abductors (APL/APB and ADM), so they do not need a dorsal interosseous. All interossei are supplied by the deep branch of the ulnar nerve (C8–T1), so finger abduction and adduction are the clinical tests of ulnar motor function.

Parts & subdivisions

  1. Dorsal interossei (×4)
    Bipennate. Abduct the index, middle and ring fingers from the axis of the middle finger. The middle finger has two, one on each side.
  2. Palmar interossei (×3)
    Unipennate. Adduct the index, ring and little fingers toward the middle finger.

Anatomy

Origin

Dorsal: adjacent sides of two metacarpals. Palmar: the palmar surface of the 2nd, 4th and 5th metacarpals (the side facing the middle finger).

Insertion

Bases of the proximal phalanges and the extensor expansions of digits 2–5.

Action

Dorsal: abduction of the digits. Palmar: adduction of the digits. Both: MCP flexion and IP extension.

Innervation

Deep branch of the ulnar nerve.

Nerve roots

C8–T1

Arterial supply

Dorsal and palmar metacarpal arteries (deep palmar arch and dorsal carpal arch).

Function

  • Abduct (dorsal) and adduct (palmar) the fingers
  • Flex the MCP and extend the IP joints
  • Stabilise the fingers for fine movements

Clinical significance

Testing the ulnar nerve

Ask the patient to spread the fingers against resistance (dorsal interossei) or to grip a card between extended fingers (card test, palmar interossei). Visible wasting of the 1st dorsal interosseous in the first web space is an early sign of ulnar neuropathy or T1 root and lower trunk lesions.

Mnemonics

PAD and DAB

Palmar ADduct, Dorsal ABduct.

Compiled from standard anatomy and physiology references — see the Muscular System sources. For education only; not medical advice.