Endotenon

The endotenon is a layer of loose connective tissue within a tendon that surrounds individual fascicles, separating them from one another and from the outer tendon sheath. It lies internal to the epitenon, which coats the entire tendon, and forms a network that helps organize the internal structure of the tendon.

The endotenon is composed of loose connective tissue containing collagen fibers and elastin, along with fibroblasts (tenocytes), small blood vessels, capillaries, and nerve fibers. This tissue forms a protective and nutritive environment around each fascicle, guiding the entry of vessels and nerves into the inner tendon and facilitating the exchange of nutrients with resident cells.

Functionally, the endotenon provides vascularization and innervation to tendon fascicles, enabling nutrient delivery and sensory input. It allows relative sliding among fascicles during movement and helps distribute mechanical load within the tendon. By housing microvasculature and nerves, it contributes to tendon healing and remodeling following injury.

Clinical relevance involves the endotenon in tendon pathology and repair. Changes in the endotenon, such as altered vascularity or disorganization of its fibrous network, can occur in tendinopathies. In surgical and therapeutic contexts, the integrity of the endotenon may influence healing, with procedures sometimes aiming to preserve or carefully manage this tissue to support recovery. See also epitenon and paratenon for the surrounding tendon interfaces.