【作者】 范娜；

【导师】 陈光雄； Michael.Morlock；

【作者基本信息】 西南交通大学 ， 机械设计及理论， 2013， 博士

【摘要】 自1970年Boutin首先将氧化铝陶瓷应用于全髋关节置换术(THA)后,陶瓷髋关节假体的使用距今已有30多年。近几年出现的第三代氧化铝陶瓷假体以其优越的摩擦学性能、极高的硬度和良好的生物相容性,日益得到医学界的认可。这些优点使其在年轻患者中得到了大量的应用。但是,近几年陶瓷假体出现的“咯吱”声异响(Squeaking,以下简称“异响”)问题逐渐引起了患者和研究者的重视。在美国和英国,使用者对关节异响很敏感,常常因关节异响而向厂商进行法律索赔,这严重阻碍了陶瓷髋关节假体的广泛应用。对髋关节异响的研究成为了全球相关学者关注的焦点。但是迄今为止,研究者对异响的产生机理认识尚浅,还没有提出控制关节异响的具体方法。所以,本课题就是针对陶瓷髋关节异响问题,运用数值模拟和实验研究两种方法较为全面地探究异响的产生机理及其相关影响因素,并最终提出减少异响发生可能性的方法。Charnley早已指出,所有常见的关节材料在摩擦过程中都有可能产生声响,所以关节异响实质是一种摩擦引起的噪声。而研究摩擦噪声的实质是研究摩擦引起的振动。在数值模拟研究中,使用ABAQUS6.7建立了陶瓷髋关节假体系统的数值模型,首先计算了各个假体部件的固有频率。髋臼组件(装配在一起的臼杯和陶瓷髋臼)的固有频率远高于异响频率而股骨组件(装配在一起的陶瓷球头和股骨柄)的固有频率非常接近异响频率,初步判断髋臼组件的振动与异响有重要关系。随后运用复特征值提取法探究了陶瓷髋关节系统在摩擦耦合下的不稳定振动模态。研究发现,当球头和髋臼配合面的摩擦系数高于临界摩擦系数时,股骨组件有发生不稳定振动的趋势,股骨组件的不稳定振动很有可能是异响产生的根本原因。为了验证数值结果,在髋关节体外模拟实验仪中测试了相应陶瓷髋关节假体系统在干摩擦下的异响频率,即不稳定振动频率。实验测得的系统不稳定模态频率非常接近数值模拟预测的不稳定模态频率,这表明数值模拟研究方法和结果是准确的,说明了股骨组件的不稳定振动确实是异响产生的根本原因。既然股骨组件的不稳定振动是异响产生的根本原因,那么股骨柄和球头必然对系统的稳定性有重要影响。作者提出通过提高系统的临界摩擦系数来提高系统的振动稳定性,从而减少异响发生的可能性。在数值模拟研究中,首先分析了系统的模态耦合过程,揭示了原始系统发生不稳定振动的临界摩擦系数。随后,探究了股骨柄的刚度对系统发生不稳定振动的临界摩擦系数的影响。研究结果表明,降低股骨柄的弹性模量,系统发生不稳定振动的临界摩擦系数降低很多；增加股骨柄的弹性模量,系统发生不稳定振动的临界摩擦有少量增加。在股骨柄中加入CoCrMo合金和316L不锈钢合金可以提高系统发生不稳定振动的临界摩擦系数,以上结果说明股骨柄的刚度对系统的稳定性有重要影响作用,提高股骨柄的刚度在一定程度上有减少异响发生可能性的趋势。陶瓷髋关节数值模拟是一种预测性的研究,可以说明股骨柄对异响的影响趋势,但是并不能证明提高股骨柄的刚度就一定可以抑制关节异响的发生。所以还需要进行髋关节体外模拟实验,研究临床应用的不同刚度的股骨柄和球头对异响的影响作用。髋关节体外模拟实验中,首先设计了获得假体系统发生不稳定振动的临界摩擦系数的实验方法。丙酮是一种挥发性的液体,将其滴入球头和髋臼的摩擦配合面中,随着液体的挥发,界面的摩擦系数缓慢增加,直到系统发生连续的、稳定的异响。第一个异响发生时界面的摩擦系数为系统发生不稳定振动的临界摩擦系数。实验结果表明,假体系统的确存在临界摩擦系数,高于临界摩擦系数,系统不一定保证有异响产生,而低于临界摩擦系数时,系统不会产生异响。这表明异响的发生不仅取决于界面的临界摩擦系数还与界面特定的润滑模态有关。随后,分别比较了3种临床中常用的不同质量和几何结构的股骨柄以及5种直径不同的球头对系统临界摩擦系数的影响。实验结果和数值模拟结果一致,股骨柄的刚度对异响的产生有重要影响作用。在同样的摩擦条件下,较长的钛合金股骨柄最容易产生异响,较长和较重的钴铬钼股骨柄其次,而短的钛合金股骨柄最不容易产生异响。这说明较高结构刚度(高的弹性模量或者更短的)的股骨柄可以减少异响发生的可能性。最小的临界摩擦系数与最大的临界摩擦系数的变化值为34%(0.29-0.39)。相比股骨柄对异响的影响,球头对异响的影响较小,其最小临界摩擦系数与最大临界摩擦系数的变化值只有20%(0.34-0.40)。中等球头直径(36mm)对应的临界摩擦系数最小,最大球头直径(44mm)对应的临界摩擦系数最大。但是,球头直径对系统发生异响时界面的临界摩擦转矩影响很大。随着球头直径的增加,系统发生异响的临界摩擦转矩也随之增加。直径40mm和44mm的球头对应的临界摩擦转矩比其它直径较小的球头大非常多。虽然大球头可以增加关节的活动度,但是大球头对应的大的摩擦转矩可能会引起其它临床问题,因为大的摩擦转矩会传递给整个假体系统。以上研究结果表明,采用刚度较大的股骨柄以及合适大小的球头可以减少异响发生的可能性。除此之外,还扩展研究了异响的相关问题,如异响只发生在“硬对硬”,一些噪声会发生在“硬对软”的配合面中,异响与摩擦力-滑动速率斜率的关系问题等。本论文通过数值模拟和体外实验两种方法较为全面地揭示了异响的产生机理及其相关影响因素,提出了减少异响发生可能性的方法。对今后研究其它关节材料或设计新的关节结构有着重要的参考意义。更多还原

【Abstract】 Alumina ceramic-on-ceramic total hip arthroplasty (THA) prosthesis have been used for more than30years since the first being introduced in1970by Boutin. In recent years, the third generation Alumina Ceramic has demonstrated excellent tribological properties, high wear resistance and good biocoMPatibility. Those advantages make ceramic hip prosthesis widely used in young patients. However, the occurrence of squeaking in ceramic-on-ceramic THA has been discussed recently as a potential worrisome problem. In America and Britain, sufferers are sensitive to squeaking. They always make claims on manufacturers for squeaking, which seriously blocks the widespread application of the ceramic hip prosthesis. The research of hip squeaking becomes a hot point for the related researchers all over the world. However, up to now, the main mechanism of squeaking generation has not been completely understood. Furthermore, there is not a realistic method for avoiding squeaking generation effectively. The aim of the present study is therefore to obtain a completed understanding of the generation mechanism and related factors for squeaking on the base of numerical and experimental studies. The other aim is to put forward a method for decreasing the susceptibility of squeaking generation.Charnley observed that the presence of frictional conditions could lead to squeaking in hip replacement patients as early as1979. Therefore, ceramic hip squeaking can be defined as a friction sound. Studying friction sound is equal to studying friction-induced vibration of the system. In the numerical study, a finite element model of a ceramic hip endoprosthesis system is established with ABAQUS6.7. The nature frequency for each prosthesis is caculated firstly. The nature frequency of acetabular component (ceramic liner assembled with shell) is much higher than squeaking frequencies, while the nature frequency of the femoral component (ceramic head assembled with stem) is close to the squeaking frequencies. Therefore, the resonance of the femoral component is considered to play an important role in the occurrence of squeaking. Afterwards, the unstable mode of the ceramic hips due to friction coupling is studied using the complex eigenvalue method. Numerical results reveal that the femoral component has a strong propensity of unstable vibration when the friction coefficient of ceramic bearings reaches to a critical value, which is considered to be the most likely mechanism for squeaking. In order to verify the numerical results, the squeaking frequencies or unstable mode frequencies of the corresponding ceramic hip prosthesis system have been tested in a hip simulator under dry friction. The unstable mode frequencies from the experiment are close to those from the numerical study. It indicates that the numerical method as well as the results is correct and the unstable vibration of the femoral component is a mian mechanism for squeaking generation.Since the unstable vibration of the femoral componet is the mechanism for squeaking generation, the stem and the head must play an important role in the stability of the system. The authors have proposed a method for decreasing the susceptibility of the squeaking generation by increasing the critical friction coefficient and the stability of the system. In the numerical study, the critical friction coefficients for unstable vibrations of the original system have been investigated by analysing the mode coupling of the system. The effect of the stem’s stiffness on the critical friction coefficient of the system has been revealed afterwards. The critical friction coefficient of the system decreases a lot with a decrease in the stem’s young’s modulus. Increasing the young’s modulus of the stem only can result in a little increase in the critical friction coefficients. The critical friction coefficients of the system are increased after adding CoCrMo alloy and316L S S in the stem. The results above indicate that the stiffness of the stem has a great influence on the stability of the system. Increasing the stiffness of the stem has an effect on decreasing the susceptibility of the squeaking generation to some extent. The numerical study of the ceramic hips stability is a method for predicting the initiation of hip squeaking, which can reveal the tendency of hip squeaking generation and the effect of the stiffness of stems on hip squeaking. Since there are always some simplifications in the finite element modeling of hip squeaking, the above numerical results must be verified by an experimental test. Therefore, more experimental studies should be carried out in the hip simulator to investigate the influence of the clinical stems with different stiffness and the head on the squeaking generation. In the experimental study, a method for obtaining the critical friction coefficient of the ceramic hips has been firstly proposed as follows:Acetone as a volatile fluid is introduced to the joint space. The friction coefficient between ceramic bearings increases gradually with time due to evaporation of acetone. When the friction coefficient reaches a certain value, continuous squeaking will occur. The friction coefficient corresponding to the onset of the first continuous squeaking is defined as the critical friction coefficient of the system. The experimental results indicate that there is a critical friction coefficient for each system. However, squeaking does not always occur above this threshold, but there is no squeaking below this threshold. This suggests that not only the friction coefficient but also particular modes of lubrication all have an effect on the onset of squeaking. The infulence of three different stems with different mass and geometric structures and five different heads with different head diameters on the squeaking generation have been investigated in the hip simulator separately. Experimental results are consistent with the numerical results. It is verified in the experimental test that the stiffness of the stem has a great infulence on the squeaking generation. Under the same friction condition, the hip with a long titanium stem is found to most likely make squeak, the hip with a longer and heavier cobalt chrome is found to likely make squeak, and the hip with a short titanium stem is found to not likely make squeak. The results suggest that a stem with high structure stiffness (higher modulus, or shorter in size) can decrease the susceptibility of the squeaking. The critical friction coefficient varied34%(0.29to0.39). CoMPared with the infulence of the stem on the squeaking, the infulence of the head diameter on the squeaking is smaller. The critical friction coefficient varied only20%(0.34to0.40). The hip system with a medium diameter (36mm) has the smallest critical friction coefficient, while the system with the biggest head diameter (44mm) has the highest critical friction coefficient. However, the head diameter has an important effect on the critical friction moment. The critical friction moment increases with bearing diameter. The critical friction moments for the head diameters of44and40mm are significantly higher than those for smaller head diameters. Although a big-size head can extend hip activity, the friction moment from a big-diameter head might produce other clinical problems because this large friction moment must be transmitted through the implanted system. All the results above reveal that using stiffer stem and proper head size can decrease the susceptibility of squeaking generation.Furthermore, another squeaking problems such as why squeaking only occurs in "hard-on-hard" bearings, while some noises occurs in "hard-on-soft" bearings and the correlation between squeaking and the slope of friction-velocity have been studied as well.In the present study, it has revealed the generation mechanism for hip squeaking and related factors affecting hip squeaking using the numerical and experimental methods. Finally, a method is put forward to decrease the susceptibility of squeaking generation. The present work is significant for the development of new hip materials and the new structure design of hips in the future.更多还原