Collagen in tendon, ligament, and bone healing. A current review

Cells that produce a particular type of collagen under normal physiologic circumstances can be induced by certain local triggers to change the amount and type of collagen synthesized. This has become most apparent during bone, tendon, and ligament healing, where cells that once produced the collagen of normal intact tissue are induced to synthesize different types of collagen at the repair site of injured tissue. For example, Type III collagen, not a major component of the extracellular matrix in normal tendons, is believed to be of great advantage during the healing process because of its ability to form rapid crosslinks and precariously stabilize the repair site. Although much is known about the gross histologic changes occurring during tissue healing, little is known about the specific role of the individual collagen types or what influences their development. This review addresses the role of collagen in normal and healing bone, tendon, and ligament. Much experimental effort is needed to uncover the distribution and function of the collagen types within connective tissue elements and the effect of growth factors on the phenotype of collagen produced in these tissue, with the ultimate goal of developing clinical manipulations that take advantage of the unique properties of each type of collagen.