Effect of mechanical set point of bone cells on mechanical control of trabecular bone architecture.

The architecture of trabecular bone is thought to be controlled by mechanosensitive bone cells, where hormones provide a background for their responses to mechanical signals. It has been suggested that, in osteoporosis, this response is hampered by changed hormonal levels, thereby increasing the mechanical set point of the cells, which would lead to bone loss. We have investigated if a temporary increase of the mechanical set point causes deterioration of trabecular bone architecture, such as seen in osteoporosis. Furthermore, the effects of a changed loading pattern were investigated for the same reason. For this purpose, we used a computer simulation model, which was based on the regulation of bone architecture by mechanosensitive osteocytes. It was found that a temporary shift of the mechanical set point causes no lasting changes in architecture. Although an increase of the mechanical set point induces bone loss, the mechanism of bone loss (trabecular thinning) differs from what is observed in osteoporosis (loss of whole trabeculae). Hence, a change of the mechanical set point alone cannot explain bone loss as seen in osteoporosis. On the other hand, the removal of load components in a particular direction resulted in irreversible loss of whole trabeculae. These results indicate that such temporary changes in loading patterns could be important risk factors for osteoporosis.