tendon

Tendons are composed of dense regular connective tissue — tightly packed parallel collagen fibers (predominantly type I collagen) aligned along the axis of tension. This arrangement gives tendons exceptional tensile strength while minimizing bulk. The collagen fibers are organized into primary, secondary, and tertiary fiber bundles surrounded by loose connective tissue (endotenon and epitenon) that carries blood vessels and nerves.

Both tendons and ligaments are dense regular connective tissues rich in collagen, but they connect different structures: tendons connect muscles to bones, while ligaments connect bone to bone. Tendons generally have higher collagen density and less elastin, reflecting their role in transmitting strong unidirectional muscle forces. Ligaments contain more elastin, allowing slight stretching to accommodate joint movement.

Tendons have a relatively poor blood supply compared to muscle, which limits the delivery of oxygen, nutrients, and inflammatory cells needed for repair. The healing process progresses through three phases — inflammatory, proliferative, and remodeling — and can take months to years. The newly formed scar tissue has disorganized collagen that is mechanically inferior to native tendon, increasing re-injury risk without proper rehabilitation.