Some Researches On Simulation Of Properties And Remodeling Of Bone Structures And Materials

As a rising edge and cross discipline, Biomechanics is the combination and further development of many disciplines such as Biology, Physiology and Medical etc. Biomechanics seeks to understand the mechanics of living tissues in different levels such as biology individual, tissue, organ, cell and molecule. The main research content of biomechanics is the relationship among stress and motion, deformation, growth etc. The biomechanical research can help us to understand better the relationships between life phenomena and their mechanical environments, and thus, effectively to design medical devices so as to improve our life quality. Because the object of biomedical research is closely related to our lives, the biomechanics is attracting more and more attention and has permeated into every realm of our lives.The finite element method is a well-developed and efficient numerical method, which plays a very important role in modern engineering and technique and also has successful applications in biomechanics and medical engineering. In 1972, the finite element method was initially applied to the study of orthopedic biomechanics by Brekelmans et al. and Rybicki et al. to evaluate the stress in human bones, since then, the method has gotten rapid development over thirty years and has been applied to every fields of biomechanics and biomedical engineering, especially in the research of orthopedic biomechanics in which the finite element method is shown to have prominent superiority. At present, the finite element method along with theoretical and experimental research has become one of the important ways of biomechanical research. Moreover, a branch of biomechanics, i.e. computational biomechanics, has formed and become more and more active and significant.In this paper, the numerical simulation technique is used to predict the mechanical properties of bone materials and structures in addition with bone remodeling simulation. The dissertation is divided into seven chapters.The first chapter is the preface. In this chapter, the background and present status of biomechanical research are systemically introduced with the emphasis on bone mechanical research, including the composition, structure and common mechanical properties of human bone. In addition, some latest improvements in the leading edge of biomechanics such as cell biomechanics, DNA biomechanics, tissue engineering, are briefly introduced, for the purpose to have a preliminary cognition of present biomechanical research after sitting through this chapter.The chapter two is a systematic introduction of the primary bone remodeling theories at present. The developing history of bone remodeling theories is restrospected, the micromechanism of bone remodeling is discussed and the possible mechanical stimuli which may cause bone to remodel are summarized in this chapter. Finally, some applications of bone remodeling theory on clinics are introduced. The applications mainly concentrate on the design of artificial joint (especially for knee joint and hip joint), surface arthroplasty of hip joint and the design of dental implants etc.In chapter three, firstly, two common and popular bone remodeling theories which have been widely applied at home and abroad are introduced with detail; both the advantages and disadvantages of each theory are discussed. Then, based on the two theories, a new approach for the simulation of bone remodeling is proposed. The shortcomings of the existing two bone remodeling theories are overcome in the newly developed algorithm. At last, some examples which often been used in literatures are verified by the proposed algorithm in this chapter; it is proven to be effective.In chapter four, the newly proposed algorithm in chapter three is applied to the simulation of bone remodeling of peri-implant tissue surrounding dental implant with and without the consideration of osseointegration respectively. Firstly, the finite element model of implant and peri-implant bone tissue without the consideration of osseointegration is established and used to predict the density distribution of peri-implant tissue after the dental implantation. Then, the influences of two parameters in bone remodeling equation on the density distribution are preliminary discussed.As a matter of fact, the osseointegration is a very important influence factor on the stability of dental implant, and also is a significant index to evaluate a dental implant surgery. In this chapter, four dental implant FE models in different osseointegration rates (25%,50%,75% and 100%) are established respectively, for the purpose to predict the influence of osseointegration rate on density distribution of peri-implant tissue. The simulating results are compared with clinical observations. The results indicate that the osseointegration rate is not bigger always better. The density distribution with 50% osseointegration is closest one compared with clinical observation. According to literature, even clinically successful dental implant surgery, its osseointegration rate is within 50～70%. The simulation results are validated by clinical observations.In chapter five, based on reverse engineering techniques and CT&MRI images, a method to establish complex bone finite element model is proposed, and the knee joint is used to demonstrate the detail procedure. Firstly, the present methods for modeling finite element models of bone tissues are systematically introduced and summarized; furthermore, the advantages and disadvantages for each method are compared and discussed. Then, the reverse engineering technique which has been widely used in engineering is introduced in this chapter to establish the finite element model of bone and related tissues. Combined with CT&MRI images, the knee joint, which is the most complex one among all human joints, is taken as an example to show the detail procedure of how to establish the three-dimensional finite element models, including femur, tibia, patella, meniscus and articular cartilages in femur and tibia.In chapter six, the stress variation before and after bone grafting surgery of Osteonecrosis of Femoral Head (ONFH) are simulated with subject-specific finite element models of proximal femur. The bone grafting surgery is one of the main means for the treatment of ONFH in its middle stage. Even though, the underlying biomechanical mechanisms of the ONFH surgery are always deficient. The research in this chapter is a try to have a deeper understanding of the procedure of bone grafting surgery by numerical simulation. Firstly, three three-dimensional FE models, i.e. normal model, necrosis model and prosthetic model are established respectively based on CT images. Then, the mechanical properties are assigned to the three FE models based on the same CT images, in other words, the CT images are "converted" in some ways into the elastic modules used by FE models. The FE models established in this way are closer to real bone structure and the computational results established in this way can be more accurate. The analysis results of three models indicate that when the necrosis region is resected, the stresses in femoral head increase obviously, but, after the bone grafting therapy, the stresses in femoral head decrease accordingly compared with normal status. It is obvious that the bone grafting therapy can effectively recover the mechanical properties of femoral head. The numerical simulation in this paper provide the clinical basis for bone grafting therapy of ONFH, meanwhile, also provide foundation for the further design optimization of surgical plan that will be done in the future.In chapter seven, the lower extremity of human being are dynamically simulated both in level walking and deep flexion. Firstly, the full dynamic model of human lower extremity including knee joint are established by LifeMod software and used to dynamically predict the procedure in level walking and deep flexion. The contact force of tibia-femoral joint and the tensile force of four main ligaments are achieved by dynamic simulation. Furthermore, the case of ACL and PCL deficiency are simulated to evaluate the influence of ACL and PCL deficiency on the contact force and ligament tensile force.