Tendon and ligament: basic science, injury and repair

Tendons and ligaments share many similar features in structure and function. They are load-bearing structures, with tendons transmitting forces from muscle to bone and ligaments transmitting forces from bone to bone. They have specialized zones (at the myotendinous junction for tendons and at the insertion to bone for both), which manage stress loading at these specific areas. They both have a hierarchical physical structure, mainly composed of type I collagen, and both elongate with a typical stress-strain pattern. Injury to both tendons and ligaments is followed by the same pattern of healing phases and can take up to two years to remodel back to a normal structure. The major cell type is the tenocyte (specialised fibroblast) in both tendons and ligaments. They are found within an extracellular matrix. Tendinopathy causes pain and swelling within tendons. Inflammatory cells and myxoid degeneration are characteristic features, with angiogenesis and small fibre nerve growth also seen. The causes are multifactorial and brought together by several hypotheses.