The extensor digitorum longus muscle is a long, thin muscle in the anterior compartment of the leg. It plays important roles in the foot by extending all the toes (except the great toe) and dorsiflexing the foot. Activities that involve repetitive foot and toe lifting, such as stair climbing, running uphill, or kicking a ball, may strain or sprain the extensor digitorum longus muscle.
Anatomy
The extensor digitorum longus muscle arises from a long, narrow origin on the tibia’s lateral condyle, along the upper fibula’s anterior surface, and on the interosseous membrane of the leg. From its origins, its muscular belly descends the leg toward the ankle as a long, narrow strip of skeletal muscle tissue. Near the ankle, it begins to form a tendon, which crosses the ankle and passes deep to the superior and inferior extensor retinaculum and superficial to the joint capsule of the ankle. At this point, the tendon divides into four distinct branches, which cross the dorsum of the foot and insert at the middle and distal phalanges of the second through fifth toes.
Physiology
The extensor digitorum longus muscle performs two major functions in the foot: extension of the toes and dorsiflexion of the foot at the ankle. Like all muscles, the extensor digitorum longus muscle contracts, pulling its insertions closer to its origins. This contraction extends the second through fifth toes at the interphalangeal and metatarsophalangeal joints by pulling the middle and distal phalanges toward the dorsum of the foot. The four tendons pull on each toe with about the same force, making it difficult to extend only one toe at a time. The toes are extended during the pushing-off phase of walking, when the ankle is raised and the toes extend as the last part of the foot to grip the floor.
The extensor digitorum longus muscle also works with other muscles of the anterior compartment — namely the tibialis anterior, extensor hallucis longus, and the fibularis tertius — to dorsiflex the foot at the ankle. These muscles all pull their insertions on the dorsum of the foot toward the anterior surface of the leg, lifting the foot from the ground. This motion is used in running and walking to prevent you from tripping over your toes.