Loading of healing bone, fibrous tissue, and muscle: implications for orthopaedic practice.

One of the most important concepts in orthopaedics in this century is the understanding that loading accelerates healing of bone, fibrous tissue, and skeletal muscle. Basic scientific and clinical investigations have shown that these tissues respond to certain patterns of loading by increasing matrix synthesis and in many instances by changing the composition, organization, and mechanical properties of their matrices. Although new approaches to facilitate bone and fibrous tissue healing have shown promise (e.g., the use of cytokines, cell transplants, and gene therapy), none has been proved to offer beneficial effects comparable to those produced by loading of healing tissues. For these reasons, patients with musculoskeletal injuries and those who have recently undergone surgery are now being treated with controlled physical activity that loads their healing tissues. Evaluation of new approaches to the promotion of healing of bone, fibrous tissue, and muscle should include consideration of the effects of loading on tissue repair and remodeling.