The flexor hallucis longus is a muscle in the lower leg and foot, playing a role in human movement. Understanding its location and function provides insight into its importance for daily activities.
Where It’s Found
The flexor hallucis longus muscle is located in the deep compartment of the posterior lower leg. It originates primarily from the distal two-thirds of the posterior surface of the fibula. Additional fibers arise from the lower part of the interosseous membrane, a fibrous sheet connecting the tibia and fibula, and from the fascia covering the tibialis posterior muscle.
From its origin, the muscle’s fibers run obliquely downward, converging into a long tendon. This tendon then travels behind the medial malleolus, the bony bump on the inside of the ankle, passing through a specialized tunnel that includes grooves on the tibia and talus bones. As it enters the sole of the foot, the tendon continues forward, running beneath the sustentaculum tali, a shelf-like projection on the heel bone. Finally, the tendon inserts into the base of the distal phalanx of the great toe.
What It Does
The main function of the flexor hallucis longus is to flex the great toe at all its joints. This action is particularly important during activities like pushing off the ground while walking, running, or jumping, as the big toe is the last part of the foot to leave the surface. The muscle helps stabilize the first metatarsal head and maintains contact between the big toe’s pad and the ground during movements such as standing on tiptoes.
The flexor hallucis longus also contributes to plantarflexion of the ankle, which is the motion of pointing the toes downward. While its contribution to ankle plantarflexion is less significant than larger calf muscles, it still plays a supportive role. Furthermore, this muscle aids in supporting the medial longitudinal arch of the foot, acting as a “bowstring” to maintain the arch’s structure during weight-bearing activities.
Common Problems
The flexor hallucis longus can develop various issues, often due to repetitive stress or overuse. One common condition is tendinitis, which involves inflammation and irritation of the tendon. This is frequently observed in athletes, especially ballet dancers, who perform repeated forceful push-off movements or prolonged pointing of the toes, placing significant strain on the tendon. Symptoms typically include pain behind the medial malleolus, which may radiate to the big toe or arch of the foot.
Pain from tendinitis often worsens with activities that require pushing off the toes. Swelling in the ankle, a clicking sensation, or stiffness in the big toe joint can also occur. Another issue is entrapment, where the tendon gets compressed as it passes behind the ankle or under the sustentaculum tali. This compression can lead to pain, clicking, or a locking sensation in the big toe, affecting mobility and daily function.