Dorsal interossei muscles of hand

The dorsal interossei muscles of hand are a group of four bipennate intrinsic hand muscles, located in the spaces between the metacarpal bones. Each muscle typically arises with two heads from the adjacent sides of two metacarpals. They primarily insert into the bases of the proximal phalanges and the extensor expansion (dorsal aponeurosis) of the index, middle, and ring fingers.

• First dorsal interosseous muscle: Situated in the first metacarpal space (between the thumb and index finger), it originates from the adjacent sides of the first and second metacarpal bones. It inserts into the radial side of the base of the proximal phalanx of the index finger and its extensor hood.

• Second dorsal interosseous muscle: Located in the second metacarpal space, it arises from the adjacent sides of the second and third metacarpal bones. It inserts into the radial side of the base of the proximal phalanx of the middle finger and its extensor hood.

• Third dorsal interosseous muscle: Found in the third metacarpal space, this muscle originates from the adjacent sides of the third and fourth metacarpal bones. It inserts into the ulnar side of the base of the proximal phalanx of the middle finger and its extensor hood.

• Fourth dorsal interosseous muscle: Positioned in the fourth metacarpal space, it arises from the adjacent sides of the fourth and fifth metacarpal bones. It inserts into the ulnar side of the base of the proximal phalanx of the ring finger and its extensor hood.

Actions

Functionally, the primary role of the dorsal interossei is to abduct (spread) the fingers away from the midline of the hand (which passes through the middle finger). Additionally, by their connection to the dorsal aponeurosis, they assist in flexion at the metacarpophalangeal (MCP) joints and extension at the interphalangeal (IP) joints.

Innervation

All dorsal interossei muscles of hand are innervated by the deep branch of the ulnar nerve (fibers from spinal segments C8 and T1).