Quadratus Plantae
Foot · Lower Limb
The quadratus plantae, also called the flexor accessorius, is a muscle of the second plantar layer unique to the foot. It arises by two heads from the medial and lateral plantar surfaces of the calcaneus and inserts onto the lateral margin of the flexor digitorum longus tendon before that tendon divides. Its function is not to flex a toe directly but to assist flexor digitorum longus, and crucially to correct the oblique line of pull of that tendon so the toes flex straight rather than being drawn medially. It is supplied by the lateral plantar nerve (S2-S3). Because the long flexor enters the sole obliquely from the medial side, this muscle is essential for balanced, effective toe flexion.
Origin, Insertion, Action & Nerve
Origin
Medial and lateral plantar surfaces of the calcaneus
Insertion
Lateral margin of the flexor digitorum longus tendon
Action
Assists flexor digitorum longus in flexing toes 2–5 and corrects its oblique line of pull
Nerve
Lateral plantar nerve (S2–S3)
Attachments explained
The Quadratus Plantae 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 and lateral plantar surfaces of the calcaneus
Insertion
Lateral margin of the flexor digitorum longus tendon
Action & function
When the Quadratus Plantae contracts, it produces the following movement: Assists flexor digitorum longus in flexing toes 2–5 and corrects its oblique line of pull.
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 Quadratus Plantae 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 Quadratus Plantae, impairing the movements it normally produces (assists flexor digitorum longus in flexing toes 2–5 and corrects its oblique line of pull). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Quadratus Plantae (the OIANS method)
Learn the quadratus plantae by its purpose rather than a joint action, since it attaches to a tendon rather than a bone of the toe. The flexor digitorum longus tendon crosses the sole obliquely from the medial malleolus, so left alone it would pull the toes medially. The quadratus plantae grips that tendon and straightens its pull, which is why it is nicknamed flexor accessorius.
Fix its two-headed calcaneal origin and lateral plantar nerve supply as second-layer features, alongside the lumbricals that also spring from the same long flexor tendons. Framing it as the muscle that redirects a borrowed tendon gives it a memorable role and explains why damage here degrades the precision of toe flexion even when the long flexor is intact.
Frequently asked questions
Where is the Quadratus Plantae located?
The Quadratus Plantae is a muscle of the Foot group, located in the Lower Limb.
What is the origin of the Quadratus Plantae?
Medial and lateral plantar surfaces of the calcaneus
What is the insertion of the Quadratus Plantae?
Lateral margin of the flexor digitorum longus tendon
What movements does the Quadratus Plantae produce?
Assists flexor digitorum longus in flexing toes 2–5 and corrects its oblique line of pull
What nerve supplies the Quadratus Plantae?
Lateral plantar nerve (S2–S3)
Is the Quadratus Plantae free to study in OIANS?
The Quadratus Plantae 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
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