【作者】 连志强；

【导师】 顾元宪； 张洪武； 关红；

【作者基本信息】 大连理工大学 ， 工程力学， 2010， 博士

【摘要】 生物力学是力学与生物学、生理学以及医学等诸多学科相互结合而形成的一门新兴的边缘交叉学科。生物力学以生命体为研究对象,它从生物个体、组织、器官以及细胞和分子等不同层次上研究应力与运动、变形、生长等之间的关系。生物力学研究可以帮助我们更好地了解各种生命现象与所处力学环境之间的关系,从而有效地设计制造各种器械、设备以改善我们的生活质量。由于其研究对象与人们的生活息息相关,生物力学这门学科已经越来越多地受到人们的关注,并且渗透到人们生活中的各个领域。有限元方法是一种成熟高效的数值计算方法,在现代工程技术中发挥了巨大的作用,在生物力学和医学工程中也有许多成功的应用。自1972年Brekelmans和Rybicki等人首先将有限元法应用于骨科生物力学的研究以来,经过30多年的迅速发展,已经渗透到生物力学、生物医学工程学等研究的各个领域,特别是在骨科生物力学研究中有限元方法显示出了显著的优越性。目前,数值模拟技术已经成为和理论研究、实验研究并列的生物力学研究的重要手段之一,并且形成了计算生物力学这个重要并且非常活跃的生物力学分支学科。本文运用数值模拟技术对骨骼材料和结构的力学性质及骨重建进行了一些数值模拟研究,全文共分七章。第一章是绪论,系统地介绍了生物力学研究的发展背景及当前的研究现状,并以骨力学的研究为重点,介绍了人体骨骼的组成、结构及常用力学性质等。另外还用少量篇幅介绍了当前生物力学中的一些前沿领域的最新研究进展,如细胞生物力学、DNA力学、组织工程等,以期对当前的生物力学研究有一个初步的认识。第二章对目前主要的骨重建理论进行了系统的介绍。首先回顾了骨重建理论的发展历程,阐述了骨重建的微观机理,并对可能引起骨重建的力学激励量进行了归纳总结。最后还介绍了骨重建理论在临床上的一些应用,这些应用主要集中在人工关节(主要是膝关节和髋关节)设计、髋关节表面成形术、种植牙中种植体的设计等方面。在论文的第三章,首先详细介绍了目前国内外应用比较广泛的两种基本的骨重建理论,并阐述了其各自的优缺点,然后在这两种骨重建理论的基础上,发展了一种新的模拟骨重建的算法,该算法有效克服了上述两种骨重建理论中存在的缺点,最后用文献中的几个算例对本文提出的骨重建算法进行了验证,证明了本文提出的算法的有效性。第四章应用本文第三章中提出的骨重建算法分别对考虑骨结合和不考虑骨结合两种情况下种植牙周围的骨重建现象进行了数值模拟。首先建立了不考虑骨结合的种植体及周围骨骼组织的有限元模型,对种植体植入后种植牙周围骨骼组织的密度分布情况进行了数值模拟,并对骨重建方程中的两个控制参数对骨密度分布的影响进行了初步的探讨。事实上,骨结合率是影响种植牙稳定性的一个重要因素,也是衡量种植牙手术成败的重要指标之一。本章还通过建立四种不同的骨结合率(25%、50%、75%、100%骨结合)的种植体模型,模拟了骨结合率对种植牙周围骨组织的密度分布情况的影响并与临床观察进行了比较。模拟结果表明,骨结合率并不是越大越好,当骨结合率为50%时,种植体周围骨组织的密度分布情况与临床观察最为接近。文献报道临床上比较成功的种植牙手术,其骨结合率均在50-70%之间,这也验证了本章的模拟结果。第五章基于逆向工程技术和医学CT&MRI图像数据,提出了建立人体复杂骨骼三维有限元模型的一种一般方法,并以人体膝关节为例,对建立模型过程进行了详细的说明。本章首先对目前建立骨骼有限元模型的方法进行了系统的归纳与总结,并比较了各方法的优缺点,还详细介绍了目前国内外在建立膝关节有限元模型方面的一些研究进展；然后将在工程领域中广泛应用的逆向工程技术引入骨骼系统建模中来,结合CT&MRI等医学图像数据,以人体关节中最为复杂的膝关节为例,详细讲述了利用逆向工程技术建立了人体膝关节的三维有限元模型的过程,该模型包括股骨、胫骨、髌骨、股骨下软骨、胫骨平台软骨、半月板。在第六章中,利用第五章中的逆向工程建模技术,通过建立特定个体(Subject-Specific)的股骨近端的有限元模型,模拟了股骨头缺血性坏死骨瓣移植前后股骨近端应力的变化情况。骨瓣移植术是治疗中期股骨头缺血性坏死的主要手段之一,但这种手术方法一直缺乏相应的生物力学理论基础。本章试图通过数值模拟骨移植前后股骨受力状态的变化来加深对这一手术的认识。首先基于医学CT图像数据分别建立了正常、坏死及修复的股骨头三维有限元模型；并基于同样的医学图像数据分别对三个有限元模型的材料参数进行设置,即将CT图像数据通过一些方法“转换”为有限元模型的弹性模量。用该方法得到的有限元模型与真实的骨骼结构更为接近,计算结果也更为准确。对三个不同模型的有限元分析结果表明,在切除掉坏死区域后,股骨头所受应力有显著增加,而进行骨移植手术后,股骨头部应力相应地减小。很明显,对坏死的股骨头进行骨瓣移植修复能有效地恢复股骨头部的力学性能,使其受力状态与正常股骨更为接近。本文的数值模拟为股骨头缺血性坏死骨瓣移植手术提供了临床依据,同时为将来进一步的手术方案优化提供了基础。第七章对人体下肢的平地行走及弯曲过程进行了动力学模拟。首先利用LifeMod软件建立了包括膝关节在内的完整的人体下肢动力学模型,并用该模型对人体平地行走及下肢弯曲过程进行了动力学模拟。得到了在人体平地行走及弯曲过程中胫-股关节的接触力及膝关节四条主要韧带张力的变化情况,并对ACL和PCL韧带缺损对胫-股关节接触力及其它韧带张力的变化情况进行了动力学模拟。更多还原

【Abstract】 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.更多还原