Flexor hallucis longus muscle
|Flexor hallucis longus muscle|
The mucous sheaths of the tendons around the ankle. Medial aspect. (Flexor hallucis longus visible at bottom center.)
|Latin||Musculus flexor hallucis longus|
|Origin||fibula, posterior aspect of middle 1/3|
|Insertion||Plantar surface; base of distal phalanx of hallux|
|Peroneal artery (peroneal branch of the posterior tibial artery)|
|tibial nerve, S1 & S2 nerve roots|
|Actions||flexes all joints of the big toe, plantar flexion of the ankle joint|
|Antagonist||Extensor hallucis longus muscle|
|Anatomical terms of muscle|
The Flexor hallucis longus muscle (FHL) is one of the three deep muscles of the posterior compartment of the leg that distally attaches to the plantar surface of the hallux (great or big toe). The other deep muscles are the flexor digitorum longus and tibialis posterior; the tibialis posterior is the most powerful of these deep muscles. All three muscles are innervated by the tibial nerve which branches from the sciatic nerve.
The Flexor hallucis longus is situated on the fibular side of the leg. It arises from the inferior two-thirds of the posterior surface of the body of the fibula, with the exception of 2.5 cm. at its lowest part; from the lower part of the interosseous membrane; from an intermuscular septum between it and the Peronæi, laterally, and from the fascia covering the Tibialis posterior, medially.
The fibers pass obliquely downward and backward, where it passes through the tarsal tunnel on the medial side of the foot and end in a tendon which occupies nearly the whole length of the posterior surface of the muscle.
This tendon lies in a groove which crosses the posterior surface of the lower end of the tibia, the posterior surface of the talus, and the under surface of the sustentaculum tali of the calcaneus; in the sole of the foot it runs forward between the two heads of the Flexor hallucis brevis, and is inserted into the base of the last phalanx of the great toe. The grooves on the talus and calcaneus, which contain the tendon of the muscle, are converted by tendinous fibers into distinct canals, lined by a mucous sheath.
As the tendon passes forward in the sole of the foot, it is situated above, and crosses from the lateral to the medial side of the tendon of the Flexor digitorum longus, to which it is connected by a fibrous slip.
Usually a slip runs to the Flexor digitorum and frequently an additional slip runs from the Flexor digitorum to the Flexor hallucis. Peroneocalcaneus internus, rare,[clarification needed] arises below or outside the Flexor hallucis from the back of the fibula, passes over the sustentaculum tali with the Flexor hallucis and inserts into the calcaneum.
Similar to the flexor digitorum longus and tibialis posterior muscles, the flexor hallucis longus muscle functions to plantar flex and invert the foot. However, it is unique in that it also functions to flex the great toe and helps supinate the ankle.
After passing through the tarsal tunnel, the flexor hallucis longus tendon must curve around a bony landmark called the sustenaculum tali. Friction at this site is likely to cause plantar-surface foot pain; this condition is called "Stenosing tenosynovitis". This occurs most often in ballet dancers when they go en pointe; plantar flexion of the foot is coupled with the entire weight of the body being supported on the tips of the flexed toes. The heavy load on the FHL tendon increases the individuals risk of friction/irritation at the sustentaculum tali. Hallux saltans is a condition that develops as a result of overusing the FHL muscle. With this condition, a nodule develops along the FHL tendon which may produce a popping effect during contraction because it drags along surrounding tissues.
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