The extensor digitorum longus (EDL) is a muscle found in the lower leg, responsible for movements of the foot and toes. Its precise location and specific actions are key to understanding its role in daily mobility. It is also susceptible to various issues. Understanding its anatomy and common problems highlights its importance for lower limb health and movement.
Anatomical Location
The extensor digitorum longus is a long, thin muscle located in the anterior compartment of the lower leg. It sits laterally, meaning towards the outside, relative to the tibialis anterior muscle and runs alongside the fibula. The EDL originates from the lateral condyle of the tibia, the proximal half to two-thirds of the anterior surface of the fibula, and the upper part of the interosseous membrane, a fibrous sheet connecting the tibia and fibula.
Its fibers converge into a strong tendon as it extends towards the ankle. This tendon passes under specialized connective tissue bands at the ankle, known as the superior and inferior extensor retinacula. After crossing the ankle, the tendon divides into four distinct slips. These tendons continue across the top of the foot, inserting onto the middle and distal phalanges of the lateral four toes (digits two through five). These insertions are typically formed via triangular dorsal digital expansions, also known as extensor hoods.
Primary Functions
The extensor digitorum longus performs two primary actions: dorsiflexion of the foot and extension of the four smaller toes. Dorsiflexion lifts the front of the foot upwards, reducing the angle between the foot and the shin. This action is essential for clearing the foot from the ground during walking or running, preventing the toes from dragging. It works with other anterior compartment muscles, like the tibialis anterior, to achieve this upward movement.
The EDL also straightens the second through fifth toes. This extension occurs at both the metatarsophalangeal and interphalangeal joints. It primarily extends the toes at the metatarsophalangeal joint, contributing to full toe extension at every joint when working with other foot muscles. Its four tendons pull on each toe with similar force, making independent toe extension challenging. This muscle also contributes to foot eversion, which is the movement of turning the sole of the foot outwards.
Common Related Issues
The extensor digitorum longus, like other muscles, can be affected by various conditions, often stemming from overuse or strain. One common issue is anterior shin splints, manifesting as pain along the front of the lower leg. This condition can arise from repetitive activities or a sudden increase in physical activity, such as running downhill, placing excessive eccentric load on the dorsiflexor muscles. Pain may worsen with activity or weight-bearing exercises.
Another issue is tendinopathy or tendinitis, characterized by tendon inflammation. Symptoms include pain on the top of the foot, swelling, and stiffness. Overuse, poor foot biomechanics, or inadequate warm-up can contribute to this tendon inflammation. Muscle strain can also occur, especially with repetitive foot and toe lifting.
A more severe condition involving the EDL is foot drop, where weakness or paralysis makes it difficult to lift the front of the foot and toes. This can cause the foot to drag when walking, leading to a “steppage gait” where the leg lifts higher to avoid tripping. Foot drop is not a disease itself but rather a symptom of an underlying problem, often related to nerve injury affecting the muscles responsible for dorsiflexion, including the EDL.