Bone structure and mechanical loading: basic science and clinical implications

It is still unclear how bones manage to generate and adapt their complex trabecular structures, what exactly these structures are optimized for, and how we can recognize structures that are no longer well adapted to their mechanical demands due to bone diseases such as osteoporosis. In this paper we address these questions by discussing the results of recent studies that used micro-finite element (FE) techniques to mechanically analyze bone structures. In the first study, stress and strain distributions in bone tissue of a healthy and osteoporotic femur are calculated and it is shown that the diseased state can be recognized from these distributions. In the second study, it is shown that the calculation of bone tissue strain distributions can enhance the prediction of bone failure load for osteoporotic bones. It can also lead to a better evaluation of drug efficacy in clinical follow-up studies, as shown in the next study discussed here. In the last study, it is shown that the process that leads to bone structure formation and adaptation can be captured by computer models implementing micro-FE models and hypothetical biological rules. Based on these results we propose that the mechanical regulation of modeling and remodeling, growth and adaptation of trabecular structure can be explained with a unified theory, assuming coupling between osteoclasts and osteoblasts to occur only implicitly through the mechanics of load transfer.