First Plantar Interosseous (Foot)
Foot · Lower Limb
The first plantar interosseous is the most medial of the three plantar interossei, unipennate muscles that lie deep in the sole between the metatarsals. It arises from the medial side and base of the third metatarsal and inserts on the medial side of the proximal phalanx of the third toe. Because adduction in the foot is defined toward the axis of the second toe, its pull draws the third toe medially toward that axis, and it also flexes the metatarsophalangeal joint while extending the interphalangeal joints through the dorsal expansion. It is supplied by the lateral plantar nerve (S2, S3). Unlike the bipennate dorsal interossei, the plantar interossei each arise from a single metatarsal, matching their adducting role.
Origin, Insertion, Action & Nerve
Origin
Medial side and base of the 3rd metatarsal (unipennate)
Insertion
Medial side of proximal phalanx of the 3rd toe
Action
Adducts the 3rd toe toward the 2nd-toe axis; flexes MTP and extends IP joints
Nerve
Lateral plantar nerve (S2, S3)
Attachments explained
The First Plantar 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
Medial side and base of the 3rd metatarsal (unipennate)
Insertion
Medial side of proximal phalanx of the 3rd toe
Action & function
When the First Plantar Interosseous (Foot) contracts, it produces the following movements: Adducts the 3rd toe toward 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 First Plantar Interosseous (Foot) receives its nerve supply from the Lateral plantar nerve (S2, S3). 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 First Plantar Interosseous (Foot), impairing the movements it normally produces (adducts the 3rd toe toward the 2nd-toe axis). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the First Plantar Interosseous (Foot) (the OIANS method)
Contrast the plantar with the dorsal interossei by the mnemonic that plantar interossei adduct (PAD) and dorsal interossei abduct (DAB), always with respect to the second-toe axis. The first plantar interosseous acts on the third toe, pulling it medially toward the second toe, which is the essence of adduction in the foot.
Reinforce the structural clue: plantar interossei are unipennate and spring from only one metatarsal, whereas dorsal interossei are bipennate from two. Noting that this first plantar muscle both originates from and inserts on the third toe's ray, always on the medial side, keeps it distinct from the dorsal interosseous that abducts the same digit.
Frequently asked questions
Where is the First Plantar Interosseous (Foot) located?
The First Plantar Interosseous (Foot) is a muscle of the Foot group, located in the Lower Limb.
What is the origin of the First Plantar Interosseous (Foot)?
Medial side and base of the 3rd metatarsal (unipennate)
What is the insertion of the First Plantar Interosseous (Foot)?
Medial side of proximal phalanx of the 3rd toe
What movements does the First Plantar Interosseous (Foot) produce?
Adducts the 3rd toe toward the 2nd-toe axis; flexes MTP and extends IP joints
What nerve supplies the First Plantar Interosseous (Foot)?
Lateral plantar nerve (S2, S3)
Is the First Plantar Interosseous (Foot) free to study in OIANS?
The First Plantar 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 First Plantar Interosseous (Foot)
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