Mechanical factors in bone growth and development.

Mechanobiologic factors strongly influence skeletal ossification and regulate changes in bone geometry and apparent density during ontogeny. We have developed computer models that implement a simple mathematical rule relating cyclic tissue stresses to bone apposition and resorption. Beginning at the fetal stages of the femoral anlage, these models successfully predict the appositional bone growth and modeling observed in the development of the diaphyseal cross section. The same basic mechanobiologic rule can also predict the architectural construction of the proximal cancellous bone formed in regions of endochondral ossification. Geometry and density changes in adult diaphyseal and cancellous bone as a result of changes in physical activity can be simulated by invoking the same rule used during development. Future clinical and experimental work is needed to provide more quantitative data for mechanobiologic rules and elucidate the interactions between chemical and mechanical factors influencing bone biology.