The Extensor Digitorum Longus (EDL) is a long muscle located in the anterior compartment of the lower leg, positioned along the front and outer side of the shin. It plays a direct role in controlling the position and movement of both the ankle and the toes. Its primary function centers on facilitating foot clearance and stability during walking and other movements.
Anatomical Structure and Pathway
The Extensor Digitorum Longus originates from bony structures near the knee joint. It starts from the lateral condyle of the tibia and the upper, front portion of the fibula. It also attaches to the interosseous membrane, the connective tissue between the tibia and the fibula.
The muscle body extends downward along the front of the leg, positioned laterally to the shin bone. As it approaches the ankle joint, it tapers into a long, four-part tendon. This tendon passes underneath the extensor retinaculum, a fibrous band that keeps the tendons in place.
Past the ankle, the structure separates into four distinct tendons. These tendons insert onto the four lateral toes—the second, third, fourth, and fifth toes—bypassing the big toe. The tendons attach to the middle and distal phalanges by forming the dorsal digital expansion, which allows for broad control over the toe joints.
Primary Roles in Foot and Toe Movement
The Extensor Digitorum Longus performs two major actions foundational to normal locomotion. Its most direct function is the extension, or lifting, of the four lesser toes at the metatarsophalangeal and interphalangeal joints. This movement straightens the toes and pulls them upward toward the ankle.
The muscle also contributes significantly to the movement of the ankle joint, assisting in dorsiflexion. Dorsiflexion is the action of pulling the entire foot upward, closer to the shin. While the muscle’s primary power is in toe extension, its contribution to lifting the foot is considerable, working alongside the larger Tibialis Anterior muscle.
These combined actions are necessary for an efficient walking pattern, particularly during the swing phase of gait. As the leg swings forward, the EDL contracts to lift the toes and the front of the foot off the ground. This upward movement prevents the toes from dragging or catching on the ground, ensuring foot clearance.
During heel-strike, the EDL also plays a stabilizing role by helping to control the rate at which the forefoot lowers to the ground. This controlled lowering action prevents the foot from “slapping” down.
Common Conditions Affecting the Extensor Digitorum Longus
Overuse Injuries
The Extensor Digitorum Longus is susceptible to overuse and traumatic injuries due to repetitive ankle and toe movements. One frequent issue is tendonitis, or inflammation of the tendon, often called tenosynovitis when the protective sheath is involved. This condition commonly affects long-distance runners due to the high volume of foot dorsiflexion required over extended periods.
Repetitive motion can lead to pain and swelling along the tendon as it passes over the front of the ankle, sometimes termed “ultramarathoner’s ankle.” Overuse can also result in a muscle strain, which is a tear within the muscle fibers. Acute injuries, such as severe ankle sprains, may cause a partial tear of the EDL tendon if the foot is forced into an extreme position.
Drop Foot
Weakness or paralysis of the Extensor Digitorum Longus contributes to the functional impairment known as “drop foot.” This condition involves the inability to lift the front part of the foot. It is often caused by damage to the deep peroneal nerve, which supplies the EDL. When the foot cannot be dorsiflexed, a person must lift their knee abnormally high to prevent the toes from dragging, resulting in a characteristic “steppage” gait.
Compartment Syndrome
The EDL’s location within the restrictive anterior compartment makes it relevant to Anterior Compartment Syndrome. This condition involves increased pressure within the muscle compartment, compromising blood flow and nerve function. Although the Tibialis Anterior is often the most affected muscle, the EDL is also located within this tight space. Swelling of the EDL can contribute to the pain and dysfunction associated with this medical emergency.