Research On Computational Model For Osteoporosis In Cancellous Bone In Accordance With Bone Physiology And Its Applicaiton

Human's research regarding the relation between mechanical environment and bone's structure was from qualitative analysis to experimental research, and now to computational simulation. In 1884 Wolff suggested an important hypothesis that bone grows where is needed and resorbs where isn't needed. That is to say, bone's growth, resorption and reconstruction are all relative to its mechanical environment. People usually call it Wolff's Law. Roax (1895) set forth the principle of bone's functional adaptation, which means bone adapts to its function by practice. At the same time he indicated that by reproduction and atrophy bone has adapted to animal's living condition and accorded with the maximal-minimal criteria, i.e. it has obtained the maximal structural stiffness using the least material. The classical studies based on hypothesis of Wolff's Law show the general scheme for remodeling, which has been studied qualitatively but not quantitatively, since heavy computing power are needed to explore the implications of this theory. After 1970's, prevalent application of computer made it possible to quantify bone's functional adaptability. Computer simulation has recently been cited as the 'third method of science'after logic and experimentation. And several attempts to quantify the bone-remodeling process so as to investigate and predict the structure and remodeling behavior of bone have beenreported in the literature. At present it is a hot point to do computational simulation based on the outcomes of certain experiments. In this dissertation, a mechanical-biological factor coupled computational model at Basic Multicellular Units (BMUs) level was put forward, which can describe osteoporotic process of cancellous bone with time course based on the outcomes of some experiments. It was used to simulate osteoporosis caused by disuse, and caused by decrease in mechanical usage, and decrease in estrogen level as well. And the contributions of mechanical factor and biological factor to the development of osteoporosis were discussed. Where does bone loss in ageing adults come from? Both mechanical usage and biological factors have their contributions to this problem. Most aging adults lose momentary muscle strength and the intensity of their physical exercise becomes weaker. The effects of ageing, menopause, drug treatment are known as biological factors, which could modulate the system by means of changing mechanical thresholds, or changing the intensities of certain signals. The computational model for osteoporosis can provide theoretical basis and computational method for the treatment and prevention of osteoporosis. However, little has been done in this aspect of research all over the world. Hazelwood et al. put forward a mechanical model of bone remodeling, which obtained different dynamical response in overload and disuse, but it was difficult to realize the numerical simulation of osteoporosis caused by biological factors. Hernandez and his colleagues put much stress on biological factors, such as BMU activation frequency, bone-remodeling space, peak bone mass, menopause, mineralization lag time to bone loss. In their computational models, mechanical factors were assumed as constant. During the development of ostroporosis, the effects of mechanical factors and biological factors are coupled. It is necessary to build a mechanical-biological factor coupled computational model at Basic Multicellular Units (BMUs) level to be more in accordance with the physiological process of bone remodeling. In the first part of this dissertation, based on bone functional adaptation and Frost's Mechanostat theory, a computational model was put forward following the physiological process of bone remodeling, which can describe osteoporotic process of cancellous bone with time course. It was applied to simulate osteoporosis caused by disuse and the effects of peak bone mass on osteoporotic process of cancellous bone were investigated. The simulated osteoporotic process caused by disuse was similar to the real physiological process. Furthermore, higher peak bone mass can postpone the occurrence of osteoporosis. The state variables, parameters and control equations in this computational model are capable of describing the mechanistic and biological process in osteoporosis caused by disuse. The second part of this dissertation deals with the contributions of mechanical factor and biological factor in the osteoporotic process of cancellous bone. Based on the physiology of bone remodeling, a mechanical-biological factor coupled computational model at Basic Multicellular Units (BMUs) level was put forward, which can describe osteoporotic process of...