Simulation Of Osteoporotic Process Of Cancellous Bone With Time History

Osteoporosis is a very damageable bone disease to human health. As themechanical industry develops and improves in this century, human beingsdependent on science and technology more and more in exploring nature world. Inthe result, physical exercise is much less than ever and peak bone mass is lower,which cause kinds of bone disease just as osteoporosis.The key mechanism of bone disease like osteoporosis comes from theinharmony between the body mechanical environment and bone structure. Human'sresearch regarding the relation between mechanical environment and bone'sstructure was from qualitative analysis to experimental research, and now tocomputational simulation. The classical studies based on hypothesis of Wolff'sLaw show the general scheme for remodeling, which has been studied qualitativelybut not quantitatively, since heavy computing power are needed to explore theimplications of this theory. After 1970's, prevalent application of computer made itpossible to quantify bone's functional adaptability. And several attempts toquantify the bone-remodeling process so as to investigate and predict the structureand remodeling behavior of bone have been reported in the literature.At present it is a hot point to do computational simulation based on theoutcomes of certain experiments. In this dissertation, a computational model atBasic Multicellular Units (BMUs) level was put forward, which can describeosteoporotic process of cancellous bone with time history based on the outcomes ofsome experiments. It was used to simulate osteoporosis caused by disuse, andcaused by decrease in mechanical usage as well. And only the contributions ofmechanical factor to the development of osteoporosis were discussed.Where does bone loss in ageing adults come from? Both mechanical usageand biological factors have their contributions to this problem. Most aging adultslose momentary muscle strength and the intensity of their physical exercisebecomes weaker. The effects of ageing, menopause, drug treatment are known asbiological factors, which could modulate the system by means of changingmechanical thresholds, or changing the intensities of certain signals. Thecomputational model for osteoporosis can provide theoretical basis andcomputational 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 differentdynamical response in overload and disuse, but it was difficult to realize thenumerical simulation of osteoporosis caused. Hernandez and his colleagues putmuch stress on biological factors, such as BMU activation frequency,bone-remodeling space, peak bone mass, menopause, mineralization lag time tobone loss.In the first part of this dissertation, based on bone functional adaptation andFrost's Mechanostat theory, a computational model was put forward following thephysiological process of bone remodeling, which can describe osteoporotic processof cancellous bone with time history. It was applied to simulate osteoporosiscaused by disuse and the effects of peak bone mass on osteoporotic process ofcancellous bone were investigated. The simulated osteoporotic process caused bydisuse was similar to the real physiological process. Furthermore, higher peak bonemass can postpone the occurrence of osteoporosis. The state variables, parametersand control equations in this computational model are capable of describing themechanistic process in osteoporosis caused by disuse.In the second part, the simulation of osteoporosis of proximal femur has beendeveloped. First, bone density distribution in proximal femur was simulated withuniform strain theory combined with finite element method, which was used as theinitial structure for simulation of osteoporosis. Convergence of the result andGeneral method to simulate bone structure with finite element method wasdiscussed. Second, the computational model with time history put forward in firstpart was integrated into finite element method in order to simulate osteoporoticprocess of proximal femur in different age and degree of disuse. The outcome isvery similar to the survey data in reference. This make the simulation ofosteoporosis improved from micro to macro and from the level of point to the levelof structure and build the base of theoretical and clinical study.Computational model of osteoporotic process of cancellous bone proposed inthe dissertation can describe osteoporotic process very well and provide the theoryfoundation and analysis method for old people preventing osteoporosis.