Tendon Repair and Regeneration

To fully understand the healing and regeneration of tendons, the relevant anatomy of each of these structures must be first understood. Each tendon is made up of a hierarchical arrangement of collagen bundles. These bundles—organized in parallel—are responsible for the tendon’s tensile strength. Tendons are primarily composed of type I collagen, but they also contain small amounts of types III, IV, V, and VI collagen. Proteoglycans are also present with decorin predominating, but biglycan, lumican, and fibromodulin have been detected as well. Proteoglycans are thought to regulate the diameter of collagen fibers, separate individual fiber bundles, and minimize the shear stresses that fibers experience as they move relative to each other during normal function. Although tendons function primarily under tensile loads, they do experience compressive loads passing around skeletal prominences. Some pressures in these regions are substantial, with measurements reported in the range of 700 mmHg. Glycosaminoglycan content in these areas is elevated relative to the rest of the tendon. This is probably a functional adaptation, which allows for greater water content and secondary structural resiliency under compressive conditions.