Tendon sheath of extensor digitorum longus

The tendon sheath of the extensor digitorum longus muscle is a multilayered anatomical structure that envelops the tendons of the extensor digitorum longus muscle as they traverse the anterior compartment of the leg, pass deep to the superior and inferior extensor retinacula of the ankle, and continue onto the dorsum of the foot.

The synovial sheath begins proximal to the superior extensor retinaculum and extends distally beneath the inferior extensor retinaculum, forming a tunnel that prevents bowstringing and protects the tendons from external trauma. The sheath is continuous with the paratenon proximally and distally, and is closely associated with the retinacular structures, which act as anatomical pulleys. As the tendons of the extensor digitorum longus muscle bifurcate and diverge to the lateral four toes, the sheath may display anatomical variations in its extent and configuration.

The sheath consists of an inner synovial layer (synovial sheath) that produces synovial fluid to facilitate low-friction movement, a middle fibrous layer composed of dense regular connective tissue with collagen fibers and elastin, and an outer vascularized connective tissue layer that supports tendon nutrition and repair.