Flexor Hallucis Longus Muscle

The flexor hallucis longus (FHL) is a powerful flexor of all the joints of the great toe. It’s one of the deep group muscles of the posterior compartment of the leg.

Four muscles make up the deep group in the posterior compartment of the leg:

1. Popliteus,
2. Flexor digitorum longus,
3. Flexor hallucis longus,
4. Tibialis posterior.

Immediately after the triceps surae has delivered the thrust of plantarflexion to the ball of the foot (the prominence of the sole underlying the heads of the 1st and 2nd metatarsals), the FHL delivers a final thrust via flexion of the great toe for the pre-swing phase (toe off) of the gait cycle. When barefoot, this thrust is delivered by the great toe; but with soled shoes on, it becomes part of the thrust of plantarflexion delivered by the forefoot.

See Also: Gait Cycle

The tendon of the FHL passes posterior to the distal end of the tibia and occupies a shallow groove on the posterior surface of the talus, which is continuous with the groove on the plantar surface of the sustentaculum tali. The tendon then crosses deep to the tendon of the flexor digitorum longus in the sole of the foot. As it passes to the distal phalanx of the great toe, the FHL tendon runs between two sesamoid bones in the tendons of the flexor hallucis brevis. These bones protect the tendon from the pressure of the head of the 1st metatarsal bone.

Flexor Hallucis Longus Muscle Anatomy

Origin	Inferior two thirds of posterior surface of fibula Inferior part of interosseous membrane
Insertion	Plantar surface of base of distal phalanx of great toe
Innervation	Tibial nerve (L4, L5, and S1)
Blood Supply	Muscular branch of peroneal and posterior tibial artery
Action	Flexes great toe at all joints and plantar flexes ankle joint; Supports medial longitudinal arch of foot

See Also: Anterior Compartment of Leg

Flexor Hallucis Longus Pain

Flexor hallucis longus pain is a condition experienced primarily by athletes, including ballet dancers and runners. Tendinopathy and other dysfunctions of the FHL is due to the repetitive forceful plantarflexion that cause a friction of the tendon or elongated muscle belly in the fibro-osseus tunnel.

To test the FHL, the distal phalanx of the great toe is flexed against resistance; if normal, the tendon can be seen and palpated on the plantar aspect of the great toe as it crosses the joints of the toe.

Flexor hallucis longus pain can be treated by Strengthening and Stretching exercises of the muscle. If patient’s fail to have significant improvement in symptoms and functional limitations with conservative management, surgical Intervention can be dine by FHL muscle belly partial resection to decrease impingement of the muscle belly in the tendon sheath or by Extensive tenosynovectomy through arthroscopic surgery.

References & More

1. Clinically Oriented Anatomy – 8th Edition
2. Newman DP, Holkup KC, Jacobs AN, Gallo AC. Recalcitrant Flexor Hallucis Longus Dysfunction: A Case Study Demonstrating the Successful Application of an Adaptable Rehabilitation Program With a Two-Year Follow-Up. Cureus. 2021 Apr 6;13(4):e14326. doi: 10.7759/cureus.14326. PMID: 34079644; PMCID: PMC8159326. Pubmed
3. Flexor hallucis longus – Physiopedia