The Flexor Digitorum Longus (FDL) is a muscle located in the lower leg and foot, playing a fundamental role in foot mechanics. It is a key component for various movements, contributing significantly to how individuals interact with their environment.
Anatomical Placement
The flexor digitorum longus muscle originates from the medial part of the posterior surface of the tibia, which is the larger of the two bones in the lower leg. Its origin lies inferior to the soleal line, a ridge on the tibia.
From this origin, the muscle fibers extend downwards, positioned within the deep posterior compartment of the leg. This deep location places it beneath more superficial muscles like the gastrocnemius and soleus.
As the muscle descends, it forms a long tendon that passes behind the medial malleolus, the bony prominence on the inside of the ankle. This tendon then enters the sole of the foot, where it divides into four distinct tendons. These four tendons insert onto the plantar surface at the base of the distal phalanges of the second, third, fourth, and fifth toes.
Primary Actions
The primary action of the flexor digitorum longus is the flexion of the lateral four toes. This curling motion occurs at both the interphalangeal joints (the joints within the toes) and the metatarsophalangeal joints (the joints connecting the toes to the foot).
Beyond toe flexion, the flexor digitorum longus also contributes to other movements of the foot. It assists in plantarflexion of the ankle, which points the foot downward. Due to its anatomical attachments and its course around the medial malleolus, it also aids in the inversion of the foot, turning the sole inward.
Functional Contribution to Movement
The actions of the flexor digitorum longus are important in many everyday movements, particularly those involving propulsion and balance. During walking and running, this muscle helps the toes grip the ground and thrust the body forward during the push-off phase. This gripping action supports generating power and maintaining forward momentum.
The muscle also plays a role in maintaining balance and stability. By allowing the toes to curl and grip, it helps the foot adapt to varied terrain, providing a stable platform for the body. The muscle’s function in gripping the ground is also important for postural balance during standing.