Third Dorsal Interosseous (Foot)
Foot · Lower Limb
The third dorsal interosseous of the foot is a bipennate muscle in the interval between the third and fourth metatarsals, arising from their adjacent surfaces. It inserts on the lateral side of the proximal phalanx of the third toe and therefore draws that toe laterally, away from the second-toe axis that defines abduction in the foot. In common with the other interossei, it also flexes the metatarsophalangeal joint and contributes to extension of the interphalangeal joints through the extensor expansion. It is supplied by the lateral plantar nerve (S2, S3). Together with the plantar interossei, it fine-tunes toe position and helps stabilise the forefoot during the stance and push-off phases of gait.
Origin, Insertion, Action & Nerve
Origin
Adjacent sides of the 3rd and 4th metatarsals (bipennate)
Insertion
Lateral side of proximal phalanx of the 3rd toe
Action
Abducts the 3rd toe from the 2nd-toe axis; flexes MTP and extends IP joints
Nerve
Lateral plantar nerve (S2, S3); first and second also receive the deep fibular nerve
Attachments explained
The Third Dorsal Interosseous (Foot) 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 metatarsals (bipennate)
Insertion
Lateral side of proximal phalanx of the 3rd toe
Action & function
When the Third Dorsal Interosseous (Foot) contracts, it produces the following movements: Abducts the 3rd toe from the 2nd-toe axis; flexes MTP and extends IP joints.
As part of the Foot group of the Lower 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 (Foot) receives its nerve supply from the Lateral plantar nerve (S2, S3); first and second also receive the deep fibular nerve. This nerve carries fibres from spinal segment(s) S2, S3.
Because a muscle can only contract when its nerve is intact, injury to the Lateral plantar nerve or to its spinal roots (S2, S3) can weaken or paralyse the Third Dorsal Interosseous (Foot), impairing the movements it normally produces (abducts the 3rd toe from the 2nd-toe axis). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Third Dorsal Interosseous (Foot) (the OIANS method)
Place this muscle by its target toe. Because it inserts on the lateral side of the third toe and abduction is judged from the second toe, its pull moves the third toe laterally, spreading it away from the second. Reasoning from the insertion side keeps you from confusing it with the adducting plantar interosseous that acts on the same digit from the medial side.
Simplify the nerve story from here on: the third and fourth dorsal interossei lack the deep fibular contribution, so they are supplied by the lateral plantar nerve alone. Memorising that the extra dorsal twig stops after the second interosseous gives you a clean rule for the whole group and marks the third as the first purely plantar-supplied member.
Frequently asked questions
Where is the Third Dorsal Interosseous (Foot) located?
The Third Dorsal Interosseous (Foot) is a muscle of the Foot group, located in the Lower Limb.
What is the origin of the Third Dorsal Interosseous (Foot)?
Adjacent sides of the 3rd and 4th metatarsals (bipennate)
What is the insertion of the Third Dorsal Interosseous (Foot)?
Lateral side of proximal phalanx of the 3rd toe
What movements does the Third Dorsal Interosseous (Foot) produce?
Abducts the 3rd toe from the 2nd-toe axis; flexes MTP and extends IP joints
What nerve supplies the Third Dorsal Interosseous (Foot)?
Lateral plantar nerve (S2, S3); first and second also receive the deep fibular nerve
Is the Third Dorsal Interosseous (Foot) free to study in OIANS?
The Third Dorsal Interosseous (Foot) is always free to browse. Its full origin, insertion, action and nerve details are open to everyone in the Muscle Directory. Quiz and Flashcard practice for the Lower Limb is part of the one-time Lifetime upgrade, though; only the Upper Limb decks are free to test yourself on.
Related muscles
Study the Third Dorsal Interosseous (Foot)
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