The flexor digitorum longus is an important deep muscle of the posterior compartment of the leg, responsible for plantarflexion of the foot and flexion of the lateral four digits. It plays a critical role in supporting the medial longitudinal arch of the foot.
The flexor digitorum longus (m. flexor digitorum longus) is located in the deep layer of the posterior compartment of the leg. Precise knowledge of its attachments is essential for understanding its biomechanics.
Origin: Muscle fibers originate directly from the posterior surface of the tibia. Neither the fibula nor the anterior surface of the tibia contributes to its origin.
Insertion: The tendon descends into the foot and divides to insert onto the distal phalanges of the lateral four digits (II–V).
Biomechanical Functions
Due to its anatomical path and insertion points, the muscle performs several critical functions:
Toe flexion: Specifically flexes the distal phalanges of digits II, III, IV, and V.
Foot plantarflexion: Contributes to general plantarflexion of the ankle joint.
Arch support: Actively supports the medial longitudinal arch, preventing its collapse under load.
Innervation and Blood Supply
Nerve regulation and blood supply are provided by the major neurovascular structures of the posterior leg:
Innervation: Supplied by branches of the tibial nerve (n. tibialis), involving nerve roots from spinal segments L₄–S₂.
Blood supply: Arterial blood is delivered via the posterior tibial artery (a. tibialis posterior).
Mnemonic
Remember the insertion simply: the muscle works for 4 digits (2nd through 5th), reaching all the way to their tips (distal phalanges) to ensure a secure grip of the foot.
Frequently asked questions
Through which osteofibrous canal does the tendon of the flexor digitorum longus enter the foot?
The tendon passes from the leg into the foot through the medial malleolar canal (canalis malleolaris medialis). From this canal, it continues into the tarsal tunnel (canalis calcaneus) to reach the plantar region.
With which tendon does the m. flexor digitorum longus cross paths in the sole of the foot?
In the sole of the foot, the tendon of the flexor digitorum longus crosses superficial to the tendon of the flexor hallucis longus (m. flexor hallucis longus). This intersection is known as the plantar chiasm (chiasma plantare), where the m. flexor hallucis longus tendon runs deep to the flexor digitorum longus tendons.
Which intrinsic foot muscles originate from the tendons of the flexor digitorum longus?
The lumbrical muscles (mm. lumbricales) originate from the tendons of the flexor digitorum longus. Each lumbrical arises from the adjacent sides of the tendons destined for digits II–V and passes to the dorsal digital expansion of the proximal phalanges.
Which muscle attaches to the tendon of the flexor digitorum longus to adjust its line of pull?
The quadratus plantae muscle (m. quadratus plantae, also known as m. flexor accessorius) inserts into the lateral margin of the flexor digitorum longus tendon. This muscle straightens the oblique pull of the flexor digitorum longus toward digits II–V and enhances their flexion.
Which bone serves as the origin for the flexor digitorum longus?
The muscle originates strictly from the posterior surface of the tibia.
Which digits does this muscle flex?
It is responsible for flexing the second through fifth (II–V) digits of the foot. The hallux (great toe) has its own dedicated flexor.
Which nerve innervates the m. flexor digitorum longus?
Innervation is provided by the tibial nerve (n. tibialis, spinal segments L₄–S₂).
Go deeper
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Omohyoid muscle (m. omohyoideus) and its intermediate tendon