Flexor Digitorum Longus
Leg · Lower Limb
The flexor digitorum longus is one of the three deep muscles of the posterior compartment of the leg, lying on the medial side. It arises from the posterior surface of the tibia below the soleal line, and its tendon passes behind the medial malleolus, crosses the sole, and divides into four slips that insert on the bases of the distal phalanges of the lateral four toes. It flexes those toes, assists plantarflexion of the ankle, and helps support the longitudinal arches, gripping the ground to give stability during standing and walking. It is supplied by the tibial nerve (S2, S3). In the sole its tendon is joined by the quadratus plantae, which corrects its oblique line of pull.
Origin, Insertion, Action & Nerve
Origin
Posterior surface of tibia (inferior to soleal line)
Insertion
Bases of distal phalanges of lateral four toes (digits 2-5)
Action
Flexion of lateral four toes (digits 2-5); plantarflexion of ankle; supports arches
Nerve
Tibial nerve (S2, S3)
Attachments explained
The Flexor Digitorum Longus 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
Posterior surface of tibia (inferior to soleal line)
Insertion
Bases of distal phalanges of lateral four toes (digits 2-5)
Action & function
When the Flexor Digitorum Longus contracts, it produces the following movements: Flexion of lateral four toes (digits 2-5); plantarflexion of ankle; supports arches.
As part of the Leg 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 Flexor Digitorum Longus receives its nerve supply from the Tibial 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 Tibial nerve or to its spinal roots (S2, S3) can weaken or paralyse the Flexor Digitorum Longus, impairing the movements it normally produces (flexion of lateral four toes (digits 2-5)). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Flexor Digitorum Longus (the OIANS method)
Learn the flexor digitorum longus as the mirror image of the extensor digitorum longus: it too splits into four slips for toes two through five, but it flexes them and reaches the plantar surface of the distal phalanges instead of the dorsum. Because its tendon passes behind the medial malleolus and crosses the sole, it aids plantarflexion and inversion and helps the toes grip during gait.
Fix two details unique to the sole: the quadratus plantae attaches to its tendon to straighten its oblique pull, and the lumbricals arise from its four tendons. Group it with the tibialis posterior and flexor hallucis longus as the deep tibial-nerve muscles behind the medial malleolus, remembering its distinctly low S2, S3 roots to separate it from its neighbours.
Frequently asked questions
Where is the Flexor Digitorum Longus located?
The Flexor Digitorum Longus is a muscle of the Leg group, located in the Lower Limb.
What is the origin of the Flexor Digitorum Longus?
Posterior surface of tibia (inferior to soleal line)
What is the insertion of the Flexor Digitorum Longus?
Bases of distal phalanges of lateral four toes (digits 2-5)
What movements does the Flexor Digitorum Longus produce?
Flexion of lateral four toes (digits 2-5); plantarflexion of ankle; supports arches
What nerve supplies the Flexor Digitorum Longus?
Tibial nerve (S2, S3)
Is the Flexor Digitorum Longus free to study in OIANS?
The Flexor Digitorum Longus 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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