Flexor Hallucis Longus

Origin

The flexor hallucis longus muscle originates from the:

- distal two thirds of the posterior surface of the fibula;

- posterior aspect of the adjacent interosseous membrane of leg;

- adjacent intermuscular septum and crural fascia.

Insertion

The fibers of the flexor hallucis longus muscle travel inferiorly to the foot and insert, via a long tendon, onto the plantar aspect of the base of the distal phalanx of the great toe.

Key Features & Anatomical Relations

The flexor hallucis longus muscle is one of the muscles of the deep part of the posterior compartment of the leg. It is a long, narrow, bipennate type of skeletal muscle. In the distal one third of the leg, the muscle belly gives rise to a tendon that travels inferomedially towards the groove for tendon of flexor hallucis longus muscle on the talus. It hooks around it, thus changing its line of pull to a more anteroinferior direction. This tendon travels deep to the flexor retinaculum of the foot, where it passes through the tendinous sheath of flexor hallucis longus muscle.

Within the plantar part of the foot, the tendon travels anteriorly, passing along the groove for tendon of flexor hallucis longus muscle on the calcaneus. The tendon continues to travel anteriorly, passing between the distal tendons of the medial and lateral parts of the flexor hallucis brevis muscle and the sesamoid bones that are found in each of these tendons. The tendon of flexor hallucis longus then passes through the fibrous sheath that is found along the plantar aspect of the great toe and then to its insertion site.

Within the posterior compartment of the leg, the flexor hallucis longus muscle is located:

- anterior to the transverse intermuscular septum of leg and the soleus muscle;

- posterior to the tibialis posterior muscle;

- medial to the fibularis longus and fibularis brevis muscles;

- lateral to the flexor digitorum longus muscle, the posterior tibial vessels, and the tibial nerve.

Within the plantar part of the foot, the tendon of the flexor hallucis longus muscle is located:

- superficial to the flexor hallucis brevis muscle;

- deep to the abductor hallucis muscle and the tendon of the flexor digitorum longus.

The flexor hallucis longus muscle is one of five structures that pass posterior to the medial malleolus. From anterior to posterior, these are the tibialis posterior muscle, flexor digitorum longus muscle, posterior tibial artery, tibial nerve, and flexor hallucis longus muscle.

Actions & Testing

The flexor hallucis longus muscle is involved in multiple actions:

- flexes the distal phalanx at the interphalangeal joint of the great toe;

- flexes the proximal phalanx at the metatarsophalangeal joint of the great toe;

- plantarflexes the foot at the ankle joint;

- helps stabilize the longitudinal arch of the foot (Sinnatamby, 2011).

The flexor hallucis longus muscle can be tested by flexing the distal phalanx of great toe at its interphalangeal joint against resistance, while its proximal phalanx is held in position, during which its tendon can be seen and palpated (Standring, 2016).

List of Clinical Correlates

- Hallux saltans

References

Sinnatamby, C. S. (2011) Last's Anatomy: Regional and Applied. ClinicalKey 2012: Churchill Livingstone/Elsevier.

Standring, S. (2016) Gray's Anatomy: The Anatomical Basis of Clinical Practice. Gray's Anatomy Series 41st edn.: Elsevier Limited.