Fourth Dorsal Interosseous (Hand)
Hand · Upper Limb
The fourth dorsal interosseous is a bipennate muscle arising from the adjacent sides of the fourth and fifth metacarpals and inserting into the extensor expansion and base of the proximal phalanx of the ring finger. It abducts the ring finger away from the axial line of the hand (following DAB, Dorsal ABduct) and flexes the metacarpophalangeal joint while extending the interphalangeal joints. It is supplied by the deep branch of the ulnar nerve (C8, T1).
Origin, Insertion, Action & Nerve
Origin
Adjacent sides of the 4th and 5th metacarpals (bipennate)
Insertion
Extensor expansion and base of proximal phalanx of the ring finger
Action
Abducts the ring finger 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 Fourth 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 4th and 5th metacarpals (bipennate)
Insertion
Extensor expansion and base of proximal phalanx of the ring finger
Action & function
When the Fourth Dorsal Interosseous (Hand) contracts, it produces the following movements: Abducts the ring finger 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 Fourth 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 Fourth Dorsal Interosseous (Hand), impairing the movements it normally produces (abducts the ring finger 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 Fourth Dorsal Interosseous (Hand) (the OIANS method)
Place the fourth dorsal interosseous last in the DAB series: it spreads the ring finger away from the middle-finger axis, that is, toward the little finger. Its bipennate origin from the fourth and fifth metacarpals sits it on the ulnar edge of the palm's back.
Since the little finger has its own dedicated abductor (abductor digiti minimi) rather than a dorsal interosseous, learning the four dorsal interossei as serving index, middle (twice), and ring fingers closes the set cleanly. The deep ulnar nerve supply and combined action carry over from the rest of the group.
Frequently asked questions
Where is the Fourth Dorsal Interosseous (Hand) located?
The Fourth Dorsal Interosseous (Hand) is a muscle of the Hand group, located in the Upper Limb.
What is the origin of the Fourth Dorsal Interosseous (Hand)?
Adjacent sides of the 4th and 5th metacarpals (bipennate)
What is the insertion of the Fourth Dorsal Interosseous (Hand)?
Extensor expansion and base of proximal phalanx of the ring finger
What movements does the Fourth Dorsal Interosseous (Hand) produce?
Abducts the ring finger away from the axial line of the hand (DAB); flexes MCP and extends IP joints
What nerve supplies the Fourth Dorsal Interosseous (Hand)?
Deep branch of ulnar nerve (C8, T1)
Is the Fourth Dorsal Interosseous (Hand) free to study in OIANS?
Yes. The Fourth 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 Fourth Dorsal Interosseous (Hand)
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