Upper limb

Fourth Dorsal Interosseous

Musculus interosseus dorsalis IV manus

Origin

Adjacent sides of the 4th and 5th metacarpal bones (bipennate)

Insertion

Ulnar side of the base of the proximal phalanx of the ring finger, with extension into the extensor hood

Function

Abduction of the ring finger toward the ulnar side (toward the little finger)

Innervation

Ulnar nerve, deep (motor) branch

Movement & chain

Acts as a spreader of the ring finger toward the ulnar side, together with the other dorsal interossei involved in fanning out the fingers.

Palpation

Palpable in the 4th dorsal intermetacarpal space between 4th and 5th metacarpals during ring finger abduction.

Clinical

Abducts the ring finger ulnarly; key clinical muscle for assessing deep ulnar nerve branch function.

Segmental innervation

Ulnar nerve, C8-T1.

In clinical practice

Focus on hand function and edema prevention; ensure IV cannulas and splints maintain functional hand position to prevent joint contractures.

Region in the model

Upper limb