Vì vậy, rời rạc của quá trình tái tạo xương trong mô hình mô phỏng không ảnh hưởng đến những tác động lâu dài của tu sửa xương trên kiến trúc cancellous. Quá trình tái tạo mô phỏng theo ba bước: tái hấp thu của mô xương để làm cho hấp thụ sâu răng, | 252 van der Linden et al. Fig. 2. Three-dimensional computer model of a cancellous bone specimen made by using a micro-CT scanner. Fig. 3. Schematic representation in two dimensions of the simulation model of bone remodeling in cancellous bone in three dimensions. Reproduced from J. Bone Miner. Res. 2001 16 688-696 with permission of the American Society for Bone and Mineral Research. cavity or not is only determined by the thickness of the trabecula and the maximal depth of the cavity. The bone loss resulting from the formation deficit is also independent of the duration of the resorption and formation period. Therefore the discretization of the bone remodeling process in the simulation model does not affect the long-term effects of bone remodeling on the cancellous architecture. The remodeling process was simulated in three steps resorption of bone tissue to make resorption cavities a resting period and finally bone formation in the resorption cavities. The three steps in the bone remodeling model are illustrated in Fig. 3. In the first step hemispherical resorption cavities were created starting from elements in the surface of the trabeculae. These resorption cavities are distributed randomly over the surface of the trabeculae. The resorption depth of the cavities could be varied in the biologically relevant range. In the second step a check for breached trabeculae was performed. If a resorption cavity breached a trabecula that cavity was not refilled the trabecula was not repaired. This resulted in two remaining struts which were connected to the main architecture but not to each other anymore. If one of these remaining struts was breached again by a resorption cavity this resulted in a loose fragment that was not connected to the main structure anymore. These loose fragments were removed from the model. Cancellous Bone Remodeling 253 Fig. 4. Contributions of the bone loss mechanisms to this total bone loss expressed as a percentage of the total bone volume .
