The Extensor Digitorum Longus (EDL) muscle is located in the lower leg and plays a significant role in foot and toe movement. It is one of the four muscles housed within the anterior compartment of the leg, a muscular group responsible for lifting the foot. The muscle’s name itself is descriptive, translating literally to the “long extensor of the toes,” highlighting its primary function. The EDL ensures fluid and stable movement during walking and running.
Anatomical Location and Structure
The Extensor Digitorum Longus originates high up near the knee joint, including the lateral condyle of the tibia. It also secures its starting point from the upper three-quarters of the fibula’s anterior surface and the adjacent interosseous membrane, the tough tissue connecting the tibia and fibula bones. This extensive origin allows the muscle belly to run down the length of the outer front side of the leg.
As the muscle travels toward the ankle, it forms four distinct tendons. These tendons pass under the superior and inferior extensor retinacula, strong bands of fascia that hold the tendons close to the ankle bone. The tendons fan out across the top of the foot and insert onto the four smaller toes, attaching to the dorsal side of the middle and distal phalanges (toe bones).
The muscle is situated in the anterior compartment of the leg, positioned lateral to the larger Tibialis Anterior muscle. Providing the necessary electrical impulse for the EDL to contract is the deep fibular nerve, a branch of the common fibular nerve. Furthermore, the muscle receives its blood supply from branches of the anterior tibial artery, which runs through the same compartment.
Biomechanical Roles
The Extensor Digitorum Longus performs two main biomechanical actions: foot dorsiflexion and extension of the four lateral toes. Dorsiflexion is the act of lifting the entire foot upward toward the shin at the ankle joint, an action it shares with the Tibialis Anterior. This upward lift is essential for preventing the toes from dragging on the ground while walking.
The muscle’s unique function is the extension, or straightening, of the four toes (second through fifth digit). This action helps to position the toes correctly just before the foot makes contact with the ground. Without the EDL, the toes would remain curled, impairing the natural progression of the foot during movement.
The EDL is particularly active during the swing phase of the gait cycle, the period when the foot is off the ground. By initiating dorsiflexion and toe extension, the EDL ensures adequate toe clearance, preparing the foot for heel strike and the next step. It works in opposition to the calf muscles, which perform plantarflexion.
Clinical Conditions Related to the Extensor Digitorum Longus
The long course and demanding function of the EDL muscle make it susceptible to specific overuse injuries. One common issue is extensor tendinopathy, which is irritation or inflammation of the tendons on the top of the foot. This condition causes aching pain and localized swelling, often worsening with activity like running or walking uphill.
Tendinopathy is often triggered by increased training volume or by wearing shoes that are too tight. If the tendons are inflamed, it is called tendinitis; if chronic, it is termed tendinosis. Pain may be noticeable when trying to lift the toes against resistance.
The EDL is vulnerable to compartment syndrome, a serious condition involving increased pressure within the rigid anterior fascial space. Acute compartment syndrome is a medical emergency resulting from trauma or bleeding that can compress the EDL, nerves, and blood vessels, potentially leading to permanent tissue damage.
More commonly, the EDL is affected by Chronic Exertional Compartment Syndrome (CECS), an exercise-induced condition. In CECS, repetitive activity causes the muscles to swell temporarily, leading to pain, cramping, and numbness that resolves completely with rest. While the EDL can contribute to anterior shin pain, it is not implicated in Medial Tibial Stress Syndrome (MTSS), the common form of “shin splints.”