Flexor hallucis longus is one of the deep muscles of the posterior compartment of the leg.
It arises from the:
- posterior surface of the fibula along its lower two thirds
- intermuscular septum
- aponeurosis of flexor digitorum longus
The tendon passes distally, medially and deep to the flexor retinaculum. Then, it passes between the medial and lateral tubercles on the posterior surface of the talus. It turns anteroinferiorly within a groove on the plantar surface of the sustenaculum tali. Crossing deep and medial to the tendon of flexor digitorum longus - to which it gives a tendinous slip, it heads anteriorly to the great toe. It passes between two sesamoid bones before inserting into the plantar base of the distal phalanx.
Flexor hallucis longus is innervated by the tibial nerve (S2,S3).
Its actions are varied:
- flexion of all the joints of the great toe
- plantarflexion of foot
- supports the medial longitudinal arch