金属对金属人工髋关节边缘接触效应

目的 研究金属对金属人工髋关节不同行走姿态下的接触力学行为,特别是大幅度运动可能导致的边缘接触效应。方法 建立球面共型接触的髋关节有限元模型,通过改变髋臼相对股骨头的倾斜状态和对股骨头施加恒定竖直方向载荷相结合,等效模拟分析人工髋关节不同行走姿态下的接触状态。结果 髋臼相对股骨头倾角在小于约60°范围内增加时,其对应的最大接触压力呈下降趋势,接触面积有所增大;当倾角超过80°范围时,关节接触区域因靠近髋臼边缘,最大接触压力位置由初始接触点向髋臼倾斜方向移动了约6°~9°的位置,用以满足压力分布合力与外载荷的平衡,接触压力和分布范围有所增加。结论 髋臼相对股骨头较大倾斜状态极易引起不同的边缘接触现象,置换人体髋关节产生的边缘接触问题需要引起临床外科和关节制造上的重视。     

Fixation of the acetabular cup in cemented total hip replacement: improving the anchorage hole profile using finite element method.

Long-term studies have shown that failure of the acetabular component in total hip replacement increases exponentially ten years following surgery and occurs mostly at the bone-cement interface. During the cemented fixation of the acetabular cup, straight anchorage holes, 3-15 mm diameter and 3-20 mm deep, are drilled in the acetabulum in order to increase torsional resistance at the bone-cement interface. The aim of this paper is to provide guidelines for improving the profile of anchorage holes. Results from our finite element models show that the efficiency of anchorage holes may be improved if they are drilled perpendicularly to the acetabulum floor and if they have chamfered necks. A 10 degree inclination of the anchorage hole increases Von Mises stress in the cement mantle by 6% while creating chamfered anchorage holes, instead of straight holes, decreases it by 14%. Increasing depth of anchorage holes does not improve efficiency.     

非球面人工髋关节接触力学

目的由于受制造技术的局限性、可能的设计优化考虑以及临床应用的磨损等因素影响,人工髋关节轴承表面表现为非球面几何特征,可以利用有限元分析方法对非球面人工髋关节的接触力学行为进行研究。方法对球面网格数据模型进行非球关节面重建,研究不同取向椭球面股骨头对球面髋臼几何特征的非球面金属对金属人工髋关节的接触力学表现。结果非球面股骨头接触区域中心位置的平均曲率半径在一定范围内增大时,能有效降低相应关节接触面上的最大接触压力,同时接触面积有所增加;在同样载荷下,髋臼相对股骨头不同倾斜状态对非球面股骨头的接触压力峰值和面积影响较小,但压力分布有所不同。结论良好地控制人工髋关节的非球表面特征,有利于改善人工髋关节最大接触压力幅值大小和接触区域分布。所发展的非球面人工髋关节接触模型及数值模拟过程能够有效地运行,这为非球面关节动态接触及磨损预测问题研究提供了条件。     

活动式与固定式 UKA 衬垫的接触力学和磨损对比研究

目的 采用计算机模拟方法对比研究 ISO 14243 - 1 ∶ 2009 力控制标准测试条件下单髁膝关节置换术(unicompartmental knee arthroplasty,UKA)活动式与固定式衬垫的接触力学和磨损性能。 方法 采用有限元方法分析两种衬垫在测试条件下的接触应力和 von Mises 应力,并采用磨损预测模型模拟 5 MC(million cycles, 百万次循环)步态周期工况获得两种衬垫的线性磨损深度、磨损体积。 结果 磨损前活动式与固定式衬垫的最大接触应力分别为 15. 7、44. 3 MPa,最大 von Mises 应力分别为 11. 94、23. 33 MPa。 随着磨损加剧,活动式衬垫的最大接触应力和 von Mises 应力先减小后趋于稳定,而固定式衬垫的基本保持不变。 固定式衬垫的线性磨损深度为活动式的1. 5 倍,但活动式衬垫的磨损体积是固定式的 5. 4 倍,且活动式衬垫的背部磨损体积占其总磨损体积的 70% 。 结论 与固定式 UKA 衬垫相比,活动式 UKA 衬垫具有较低的接触应力与 von Mises 应力,但有较大的磨损体积。 活动式衬垫背部磨损是磨屑增加的另一个重要来源。     

金属对金属髋关节动态边缘接触力学行为

目的研究球面共型接触人工髋关节在股骨头动态位移条件下的边缘接触力学行为。方法基于所发展的有限元球面网格数据模型,动态模拟分析金属对金属人工髋关节在给定生理位移工况条件下的接触行为和可能诱发的边缘接触现象。结果数值模拟表明,随着动态位移载荷的增加,关节接触面压力合力的垂直分力和水平分力都有上升趋势;在边缘接触过程中压力合力的垂直分力比非边缘接触情况变化趋势要缓慢,但相应的水平分力增大趋势更显著。此外,边缘接触与非边缘接触对应的接触压力分布形态与接触区域也各不相同。结论金属对金属人工关节髋臼相对股骨头过大的倾斜状态极易引起边缘接触,动态边缘接触情况下,将导致股骨头向髋臼内侧产生相对滑动及附加磨损的可能,这对临床人工髋关节磨损评估与关节制造发展提供了分析依据。     

Influence of Charnley hip neck-angle inclination on the stresses at stem/cement and bone/cement interfaces

The present work aims to elucidate the influence of neck-stem angle inclination on the principal normal and shear stress distributions and values along the interfaces of the stem/cement and bone/cement in a cemented Charnley curved back femoral component. The same stresses were also examined for the intact bone that was considered as a reference for the obtained results. The interface is considered the weakest link in the structure and its endurance limit to failure is much less than the limit of the adjacent materials. Interface loading is by far the influential aspect governing the induced interface stresses in femoral total hip replacement. Therefore, higher values and nonuniform distribution of stresses at the interface may lead to loosening and crack initiation and propagation that usually precede the stem fracture.     

全髋关节置换术中臼杯水平位移对股骨侧非骨水泥型假体-骨界面应力影响的有限元分析

目的　利用三维有限元力学分析方法, 研究全髋关节置换术中臼杯水平位移对股骨侧非骨水泥型假体-骨界面应力分布的影响。 方法　选取正常人体的骨盆及股骨为实验对象, 螺旋CT 扫描,利用计算机仿真技术对CT图像进行三维重建,建立髋关节及股骨模型,进行全髋关节置换的模拟手术, 臼杯位置从髋关节旋转中心外侧10mm处起,水平内移,每隔2 mm为一个实验组,至内移至旋转中心内侧10 mm,共分11个实验组。加载关节负荷,观察股骨侧假体-骨界面间的Von Mises应力分布情况, 对结果进行统计分析。 结果　臼杯的水平位移没有改变股骨总体的应力云分布;各组假体-骨界面应力均值（4.728±2.152）-（5.431±2.465）MPa,均值有差异,差异有统计学意义;应力均值、极差、标准差均随内移而降低,呈高度的负相关。近端假体-骨界面的应力变化,与整个股骨的应力变化相似。 结论　假体的水平内移可以降低股骨侧假体-骨界面间的Von Mises应力,内移可以使界面的应力分布更均匀。     

UKA假体后倾角安装位置对衬垫磨损的影响

目的 研究单髁膝关节置换(unicompartmental knee arthroplasty, UKA)假体不同后倾角度安装对膝关节承载、运动及衬垫磨损的影响。方法 联合UKA骨肌多体动力学模型、有限元模型和磨损模型,分析固定式UKA假体5种后倾角安装位置情况对术后膝关节力和运动、衬垫接触应力、线性磨损深度和体积磨损量的影响。结果 后倾角0°时,衬垫的最大von Mises等效应力为24.84 MPa,接触应力为47.61 MPa, 5百万次循环(million cycle, MC)周期的磨损量为47.29 mm³。随着UKA胫骨假体后倾角的增加,步态周期内旋和后移运动均增大,摆动相的内侧关节力增大,5 MC磨损周期后衬垫von Mises等效应力与接触应力显著减小,衬垫的磨损面积、最大线性磨损深度和体积磨损量随之减少。相对于后倾角0°,后倾角为3°、5°、7°时衬垫的线性磨损深度分别减小了17.8%、19.2%、20.6%;衬垫体积磨损量分别下降了24.5%、30.9%、34.3%。结论 UKA假体考虑后倾角安装超过3°时会显著增加步态周期内旋运动和后移运动,...     

The effect of motion patterns on edge-loading of metal-on-metal hip resurfacing

The occurrence of pseudotumours (soft tissue masses relating to the hip joint) following metal-on-metal hip resurfacing arthroplasty (MoMHRA) has been associated with high serum metal ion levels and consequently higher than normal bearing wear. We investigated the relationship between serum metal ion levels and contact stress on the acetabular component of MoMHRA patients for two functional activities; gait and stair descent. Four subjects with MoMHRA, who had their serum metal ion levels measured, underwent motion analysis followed by CT scanning. Their motion capture data was combined with published hip contact forces and finite element models representing 14% (peak force) and 60% (end of stance) of the gait cycle and 52% (peak force) of stair descent activity were created. The inclination angle of the acetabular component was increased by 10° in 1° intervals and the contact stresses were determined at each interval for each subject.When the inclination angle was altered in such a way as to cause the hip contact force to pass through the edge of the acetabular component edge-loading occurred. Edge-loading increased the contact stress by at least 50%; the maximum increase was 108%. Patients with low serum metal ion levels showed no increase in contact stress at peak force during gait or stair descent. Patients with high serum metal ion levels exhibited edge-loading with an increase to the inclination angle of their acetabular components. The increase in inclination angle that induced edge-loading for these subjects was less than the inter-subject variability in the angle of published hip contact forces. The results of this study suggest that high serum metal ion levels are the result of inclination angle influenced edge-loading but that edge-loading cannot be attributed to inclination angle alone and that an individual's activity patterns can reduce or even override the influence of a steep acetabular component and prevent edge-loading.     

Contact mechanics studies of an ellipsoidal contact bearing surface of metal-on-metal hip prostheses under micro-lateralization

The morphology of the contact bearing surfaces plays an important role in the contact mechanics and potential wear of metal-on-metal (MOM) hip prostheses. An ellipsoidal bearing surface was proposed for MOM hip implants and the corresponding contact mechanics were studied by using the finite element method (FEM) under both standard and micro-lateralization conditions. When under micro-lateralization, the maximum contact pressure decreased from 927.3 MPa to 203.0 MPa, with increased ellipticity ratio medial-laterally. And the contact region was found to shift from the rim of the cup to the inner region compared to the spherical design. Under standard conditions, an increasing trend of the maximum contact pressure for the acetabular component was predicted as the major radius of the ellipsoidal bearing surface was increased. Nevertheless, the maximum contact pressure reached an asymptotic value when the ellipticity ratio was increased to 1.04. Therefore it is critical to optimize the ellipticity ratio in order to reduce the contact pressure under micro-lateralization condition and yet not to cause a markedly increased contact pressure under normal condition. Additionally, the maximum contact pressure in the ellipsoidal bearing surface remained relatively constant with the increased micro-lateralization. It is concluded that an ellipsoidal bearing surface morphology may be a promising alternative by offering better contact mechanisms when micro-lateralization should occur and attributing to minimized wear.     

Ceramic bearing surfaces in total artificial joints: resistance to third body wear damage from bone cement particles

Studies of explanted Charnley hip prostheses have shown damage or scratching of the polished stainless steel femoral heads. This surface damage is probably due to third body wear by bone cement particles. Damaged femoral heads will produce increased wear rates of ultra high molecular weight polyethylene (UHMWPE) acetabular cups. Sliding wear tests carried out in the laboratory have shown that alumina ceramic counterfaces are more resistant to third body damage from bone cement particles than stainless steel counterfaces. The use of the ceramic femoral heads in artificial hip joints will help to preserve the smooth surface finish on the femoral bearing surface, which is necessary to ensure low wear rates of the UHMWPE cup throughout the lifetime of the prosthesis.     

The contact mechanics and occurrence of edge loading in modular metal-on-polyethylene total hip replacement during daily activities

The occurrence of edge loading in hip joint replacement has been associated with many factors such as prosthetic design, component malposition and activities of daily living. The present study aimed to quantify the occurrence of edge loading/contact at the articulating surface and to evaluate the effect of cup angles and edge loading on the contact mechanics of a modular metal-on-polyethylene (MoP) total hip replacement (THR) during different daily activities. A three-dimensional finite element model was developed based on a modular MoP bearing system. Different cup inclination and anteversion angles were modelled and six daily activities were considered. The results showed that edge loading was predicted during normal walking, ascending and descending stairs activities under steep cup inclination conditions (≥55°) while no edge loading was observed during standing up, sitting down and knee bending activities. The duration of edge loading increased with increased cup inclination angles and was affected by the cup anteversion angles. Edge loading caused elevated contact pressure at the articulating surface and substantially increased equivalent plastic strain of the polyethylene liner. The present study suggested that correct positioning the component to avoid edge loading that may occur during daily activities is important for MoP THR in clinical practice.     

Cam型髋关节撞击综合征关节软骨接触力学的有限元分析

目的 通过有限元方法探讨不同严重程度的Cam型髋关节撞击综合征(femoroacetabular impingement,FAI)关节软骨接触力学的变化。方法 建立正常髋关节及不同α角的 Cam型FAI髋关节三维有限元模型,计算行走、坐下、起立等日常活动下的关节软骨接触压力和应力。结果 完整步态周期加载过程中,不同α角的Cam型FAI软骨接触压力分布与正常髋关节接近,无高接触压力和Von Mises应力集中区域;坐下、起立加载过程中,Cam型FAI软骨接触压力均大于正常髋关节,且随α角的增加而增大,其接触区域主要位于髋臼缘前上方,局部出现过高压力和Von Mises应力集中。结论 Cam型FAI软骨接触力学变化的关键影响因素是运动方式,关节软骨过高的接触压力和Von Mises应力,可能是其引起软骨退变并最终导致骨性关节炎的力学原因。     

A tribological study of UHMWPE acetabular cups and polyurethane compliant layer acetabular cups

A novel design of polyurethane compliant layer acetabular cup has been developed through a series of friction, creep and wear tests. Friction tests were initially conducted on ABG standard form, polyurethane acetabular cups and an ABG standard form, UHMWPE acetabular cup for comparison. The polyurethane cups showed lower friction than the UHMWPE cup with maximum friction factors between 0. 008 and 0.02 compared with 0.035 for the UHMWPE cup. This indicated that, in the polyurethane cups, more of the load across the joint was carried by the fluid entrapped in the joint space rather than with asperity contact, compared with the UHMWPE cup. The inherent compliance of the polyurethane is used to promote elasto-hydrodynamic lubrication. However, this compliance raised concerns over excessive creep, which may in turn adversely affect tribological performance. Therefore, creep tests were undertaken on the ABG standard form, polyurethane acetabular cups followed by further friction tests. Small amounts of creep occurred in the polyurethane cups at ambient temperature, which reduced the friction slightly (maximum friction factors of 0.009) due to increased conformity between the head and the cup. However, at 37 degrees C, greater creep occurred causing pinching of the femoral head by the acetabular cup resulting in lubricant starvation and higher friction (maximum friction factors of 0.035). The design of the polyurethane cups was subsequently modified to incorporate a flared rim to eliminate the possibility of fluid starvation through pinching. Creep in polyurethane acetabular cups is also affected by the method of fixation of the cups, due to the conformity with and the stiffness of the cup backing. Hence, a one-million-cycle wear test was performed on five ABG flared form, polyurethane acetabular cups on the Mk. I Durham Hip Joint Wear Simulator to evaluate the best method of fixation for the polyurethane cups. The smallest amount of penetration, due to creep and wear, was found with cement fixation (0.30 mm penetration with cement fixation, 0.44 mm with polyethylene holder mounting, and 0.52 mm with metal shell mounting). A 4. 25-million-cycle wear test was then conducted on a further five ABG flared form, polyurethane acetabular cups with cement fixation. Five ABG standard form, UHMWPE acetabular cups were also wear-tested to 5. 0-million cycles. The mean and standard error of the wear rate for the polyurethane cups were 14.1 +/- 4.3 mg/10(6) (12.0 +/- 3.6 mm(3)/10(6)), cycles compared with 44.8 +/- 3.4 mg/10(6) (48.2 +/- 3. 7 mm(3)/10(6)), cycles for the UHMWPE cups. This study showed that the novel polyurethane-compliant layer acetabular cup with cement fixation was tribologically superior to the ABG standard form UHMWPE design currently being used clinically.     

Severe wear from retrieved alumina-on-alumina coupled implant: a case report.

This study details the in vivo wear behavior of an alumina acetabular cup and a femoral head on a retrieved non-cemented hip prosthesis. A commercial alumina ceramic-on-ceramic prosthesis was retrieved from a patient previously treated for bilateral hip arthrosis in "coxa profunda". Massive wear was found on the retrieved alumina ceramic head and acetabular cup. The total measured penetration depth was 1.9 mm while the total calculated weight loss for the acetabular cup was 6.06 g. The study underlines the head-cup instability caused by cup loosening as major cause of severe ceramic wear.     

Effect of geometric parameters in the design of customized hip implants

In this paper, the effects of geometric parameters on the development of stress in custom cementless hip implant have been studied. Taguchi methods and analysis of variance (ANOVA) were used to find out which geometric parameters are statistically significant for the maximum von Mises stresses in the hip implant. The multiple regression analysis was also performed, to replace the FE solver and accurately and quickly predict the stress values for new patients. Three parameters horizontal offset (HO), vertical offset and neck shaft angle (NSA), with three levels have been selected. Based on L9 orthogonal array, nine hip implant shapes with three different geometric parameters were modelled. Stress analysis was carried out by using finite element analysis. ANOVA results showed that HO has the maximum impact on von Mises stresses followed by the NSA. It is shown that as the HO increases, the stress at the given region increases, however, as the neck shaft (NSA) increases the stress at the given region decreases. Good agreement is found between von Mises stresses, calculated from multiple regression analysis and obtained from FE analysis. To redesign customised hip implant for the minimum stresses, the results of this work will be important.     

弯曲参数对软组织缝合过线器弯钩力学性能的影响

目的 探究弯钩偏转角和弯钩倾斜角对软组织缝合过线器弯钩力学性能的影响.方法 以远离针尖端端面(端面1)为研究对象,建立以力矩大小为因变量,弯钩偏转角和倾斜角为自变量的数学模型.探究偏转角和倾斜角为0°、10°、20°和30°时的力矩,并用数学模型求解出力矩.基于有限元分析法,使用SolidWorks软件建立偏转角和倾斜...     

Parameteric optimisation of materials for acetabular cup

This paper describes a method of parametric optimisation to determine the optimal stiffness characteristics of cement, metal backing and UHMWPE (Ultra High Molecular Weight Polyethylene) materials, which minimises the probability of fatigue fracture of cement at all interfaces with the metal backing and the bone, while limiting the amount of bone resorbed. The parameters describing the elastic moduli of cement, metal backing and UHMWPE were considered as design variables. The method was applied to an axisymmetric finite element model of acetabular cup in combination with an optimisation procedure using the ANSYS program. Young's moduli of about 0.63, 207 and 0.72 GPa are optimal materials for cement, metal backing (MB) and UHMWPE, respectively. These characteristics decreased fatigue notch factor Kf in cement by 8.2 and 10.6% and also decreased the maximum von Mises stress in cement by 21 and 27% at cement/bone and cement/metal backing interfaces, respectively. The optimal design reduces the probability of fatigue fracture of cement at all interfaces with the bone and the metal backing while limiting the amount of bone resorbed as a result of increasing von Mises stress and Kf in the central bone of the acetabulum by 34 and 30.6%, respectively.     

髋臼发育不良者全髋置换中臼杯置入位置的力学分析

目的　利用三维有限元分析方法,研究髋臼发育不良患者加深磨锉假体置入部位的髋臼骨床、使臼杯假体内移置入对髋臼假体-骨界面间的应力分布情况的影响。  方法　选取髋关节发育不良患者的骨盆为实验对象,螺旋CT做全长连续扫描,然后利用计算机仿真技术对CT图像进行三维重建,建立髋关节发育不良骨盆模型。在计算机环境中对重建模型进行髋臼磨锉,臼杯假体不同程度内移植入的模拟手术,利用有限元分析软件SolidWorks对重建模型进行有限元网格化及力学分析。  结果　臼杯假体的内移使臼杯上缘处获得骨床包容,臼杯接触面积更大,单位面积所受应力相对较少。随内移程度加大,髋臼内壁骨质突破更为明显,使髋臼顶部应力集中及其余部分应力不均愈趋明显。  结论　髋臼加深磨锉臼杯内移植入有助于改善髋关节发育不良病例行髋关节置换臼杯的骨床包容,但随内移程度的加大,髋臼内壁突破,髋臼面的应力集中,髋臼的应力分布情况明显改变,应尽量减少穿破的程度。     

轻度与重度骨关节炎膝关节的生物力学行为比较

目的 对比研究轻度与重度膝骨关节炎(knee osteoarthritis, KOA)膝关节的生物力学行为,阐述KOA进展的生物力学机制。方法 分别构建同一患者左侧轻度KOA(KL分级Ⅰ级)与右侧重度KOA(KL分级Ⅳ级)膝关节有限元模型。在材料属性、边界条件、载荷等设定相同的情况下进行有限元分析,比较轻度与重度KOA膝关节半月板、股骨软骨、胫骨软骨的接触面积、接触压及von Mises应力的变化特征。结果 重度KOA膝关节总接触面积和外侧室接触面积大于轻度KOA膝关节,而内侧间室接触面积小于轻度KOA膝关节。重度KOA膝关节半月板、股骨软骨和胫骨软骨上的接触压及von Mises应力峰值均大于轻度KOA膝关节;双膝关节外侧半月板上接触压及von Mises应力峰值均大于内侧半月板,双膝关节股骨软骨与胫骨软骨内侧间室接触压及von Mises应力峰值均大于外侧间室。结论 重度KOA膝关节应力分布不同于轻度KOA,接触面积、接触压和von Mises应力峰值的变化与半月板脱位、软骨缺损等因素相关,生物力学行为和解剖结构的改变促进了KOA进展。