Flexor digitorum longus is one of the deep muscles of the posterior lower limb. It originates from the posterior and middle third of the tibia below the soleal line, and the adjoining interosseous membrane. Its tendon passes inferiorly posterior to the medial malleolus and around the sustentaculum tali to enter the sole of the foot. In a plane more superficial to flexor hallucis, it divides into four tendons. These insert into the bases of the distal phalanges of the lateral four toes.
It is innervated by the tibial nerve (S1,S2).
Flexor digitorum longus has the following actions:
- flexion of the lateral four toes
- plantarflexes the foot at the ankle
- supports the medial longitudinal arch