First Dorsal Interosseous (Hand)
Hand · Upper Limb
The first dorsal interosseous is the largest and most superficial of the four dorsal interossei, occupying the web space between the thumb and index finger. Like the others it is bipennate, arising from the adjacent sides of the first and second metacarpals, and it inserts into the extensor expansion and base of the proximal phalanx of the index finger. It abducts the index finger away from the axial line of the hand (the middle-finger axis), following the mnemonic DAB, meaning Dorsal ABduct, and, through its extensor-expansion attachment, flexes the metacarpophalangeal joint while extending the interphalangeal joints. It is supplied by the deep branch of the ulnar nerve (C8, T1), and its wasting is an early, visible sign of ulnar neuropathy.
Origin, Insertion, Action & Nerve
Origin
Adjacent sides of the 1st and 2nd metacarpals (bipennate)
Insertion
Extensor expansion and base of proximal phalanx of the index finger
Action
Abducts the index 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 First 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 1st and 2nd metacarpals (bipennate)
Insertion
Extensor expansion and base of proximal phalanx of the index finger
Action & function
When the First Dorsal Interosseous (Hand) contracts, it produces the following movements: Abducts the index 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 First 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 First Dorsal Interosseous (Hand), impairing the movements it normally produces (abducts the index 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 First Dorsal Interosseous (Hand) (the OIANS method)
Master all four dorsal interossei with one mnemonic, DAB for Dorsal ABduct, then apply it here: the first dorsal interosseous spreads the index finger away from the middle-finger axis. Being bipennate and arising from two metacarpals gives it the bulk you can see in the web space between thumb and index.
Use this muscle as your ulnar-nerve barometer. Because it is large and superficial, its wasting is one of the earliest visible signs of ulnar neuropathy, and all the interossei share the deep branch of the ulnar nerve. Learning that shared innervation once covers the entire interosseous set.
Frequently asked questions
Where is the First Dorsal Interosseous (Hand) located?
The First Dorsal Interosseous (Hand) is a muscle of the Hand group, located in the Upper Limb.
What is the origin of the First Dorsal Interosseous (Hand)?
Adjacent sides of the 1st and 2nd metacarpals (bipennate)
What is the insertion of the First Dorsal Interosseous (Hand)?
Extensor expansion and base of proximal phalanx of the index finger
What movements does the First Dorsal Interosseous (Hand) produce?
Abducts the index finger away from the axial line of the hand (DAB); flexes MCP and extends IP joints
What nerve supplies the First Dorsal Interosseous (Hand)?
Deep branch of ulnar nerve (C8, T1)
Is the First Dorsal Interosseous (Hand) free to study in OIANS?
Yes. The First 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 First Dorsal Interosseous (Hand)
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