Anatomy OIAN Practice Test

Extensor carpi ulnaris is the muscle that inserts at the base of the fifth metacarpal, and its action is to extend the wrist while adducting the hand toward the ulna (ulnar deviation). The tendon’s placement at the base of the fifth metacarpal means when it contracts, it pulls that part of the hand toward the little finger side and simultaneously extends the wrist. That combination matches the described movement.

Extensor digitorum can extend the fingers and assist with some wrist extension, but its tendon attaches to the extensor expansions of the digits rather than the base of the fifth metacarpal, so it doesn’t produce the same ulnar deviation. Flexor digitorum superficialis is a finger flexor, not a wrist extensor, and flexes the fingers via the middle phalanges. Flexor carpi radialis flexes and abducts the wrist (radial deviation) and attaches to the bases of the second and third metacarpals, not the base of the fifth metacarpal or the action described.