NBDE Anatomy Practice Test

Abduction of the fingers is carried out by the dorsal interossei. These intrinsic hand muscles sit between the metacarpals and originate from the adjacent sides of neighboring metacarpals, then insert into the proximal phalanges and extensor expansions. When they contract, they pull the digits away from the midline of the hand (the line through the middle finger), producing finger abduction. They also assist with flexing the metacarpophalangeal joints and extending the interphalangeal joints through the extensor mechanism.

In contrast, the palmar interossei adduct toward the midline, lumbricals flex the MCP joints and extend the IP joints without causing abduction, and flexor digitorum superficialis primarily flexes the PIP joints (and MCP) rather than moving fingers laterally. So the dorsal interossei are the muscles that abduct the fingers.