Third Dorsal Interosseous (Hand)
Hand · Upper Limb
The third dorsal interosseous is a bipennate muscle arising from the adjacent sides of the third and fourth metacarpals and inserting into the extensor expansion and base of the proximal phalanx of the middle finger on its ulnar side. It abducts the middle finger toward the little-finger side (ulnarly) away from the hand's axial line, and, like all the interossei, flexes the metacarpophalangeal joint while extending the interphalangeal joints. Because the middle finger has a dorsal interosseous on each side, it is the only finger that can be abducted in both directions. It is supplied by the deep branch of the ulnar nerve (C8, T1).
Origin, Insertion, Action & Nerve
Origin
Adjacent sides of the 3rd and 4th metacarpals (bipennate)
Insertion
Extensor expansion and base of proximal phalanx of the middle finger (ulnar side)
Action
Abducts the middle finger ulnarly away from the axial line of the hand (DAB); flexes MCP and extends IP joints
Nerve
Deep branch of ulnar nerve (C8, T1)
Attachments explained
The Third Dorsal Interosseous (Hand) is defined first by where it attaches. Its origin is the more fixed anchor, usually the proximal or more stable end that stays put during contraction, while its insertion is the more mobile point that is pulled toward the origin when the muscle shortens.
Origin
Adjacent sides of the 3rd and 4th metacarpals (bipennate)
Insertion
Extensor expansion and base of proximal phalanx of the middle finger (ulnar side)
Action & function
When the Third Dorsal Interosseous (Hand) contracts, it produces the following movements: Abducts the middle finger ulnarly away from the axial line of the hand (DAB); flexes MCP and extends IP joints.
As part of the Hand group of the Upper Limb, it works alongside neighbouring muscles to generate smooth, coordinated movement and to stabilise the structures it acts on.
Nerve supply & clinical relevance
The Third Dorsal Interosseous (Hand) receives its nerve supply from the Deep branch of ulnar nerve (C8, T1). This nerve carries fibres from spinal segment(s) C8, T1.
Because a muscle can only contract when its nerve is intact, injury to the Deep branch of ulnar nerve or to its spinal roots (C8, T1) can weaken or paralyse the Third Dorsal Interosseous (Hand), impairing the movements it normally produces (abducts the middle finger ulnarly away from the axial line of the hand (DAB)). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Third Dorsal Interosseous (Hand) (the OIANS method)
Pair the third dorsal interosseous with the second: together they let the middle finger swing to either side, which is the memorable consequence of the axial line passing through that finger. This muscle applies DAB by pulling the middle finger toward the little-finger side.
Reinforce the universal interosseous pattern here rather than treating it as new material: deep ulnar nerve supply, bipennate origin from two adjacent metacarpals, and the dual action of flexing the metacarpophalangeal joint while extending the interphalangeal joints through the extensor expansion.
Frequently asked questions
Where is the Third Dorsal Interosseous (Hand) located?
The Third Dorsal Interosseous (Hand) is a muscle of the Hand group, located in the Upper Limb.
What is the origin of the Third Dorsal Interosseous (Hand)?
Adjacent sides of the 3rd and 4th metacarpals (bipennate)
What is the insertion of the Third Dorsal Interosseous (Hand)?
Extensor expansion and base of proximal phalanx of the middle finger (ulnar side)
What movements does the Third Dorsal Interosseous (Hand) produce?
Abducts the middle finger ulnarly away from the axial line of the hand (DAB); flexes MCP and extends IP joints
What nerve supplies the Third Dorsal Interosseous (Hand)?
Deep branch of ulnar nerve (C8, T1)
Is the Third Dorsal Interosseous (Hand) free to study in OIANS?
Yes. The Third Dorsal Interosseous (Hand) is free in OIANS: its full origin, insertion, action and nerve details are open to everyone in the Muscle Directory, and because it belongs to the Upper Limb it is also covered by the free Quiz and Flashcard decks. The other regions, the "All Muscles" deck, and the Progress and Explore tools are unlocked with a one-time Lifetime purchase.
Related muscles
Study the Third Dorsal Interosseous (Hand)
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