Upper limb

Third Dorsal Interosseous

Musculus interosseus dorsalis III manus

Origin

Adjacent sides of the 3rd and 4th metacarpal bones (bipennate)

Insertion

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

Function

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

Innervation

Ulnar nerve, deep (motor) branch

Movement & chain

Together with the second dorsal interosseous forms the spreading mechanism of the middle finger to both sides, functionally involved in spreading the fingers.

Palpation

Palpable in the 3rd dorsal intermetacarpal space during ulnar deviation of the middle finger.

Clinical

Abducts the middle finger ulnarly; dorsal guttering/atrophy is a classic sign of ulnar neuropathy or ALS.

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