骨水泥填充对人工关节假体置入后应力状态的影响

本研究应用光弹技术对骨水泥填充后人工关节假体的应力状态进行了观测，结果表明骨水泥固结长度增加可降低假体内侧内应力，但固结假体柄尖部则反而使假体柄中上段应力增大，易生产假体柄疲劳断裂。     

骨水泥型关节假体骨水泥-骨界面相关研究进展

骨水泥型关节假体无菌性松动是影响假体使用寿命的主要问题。假体松动翻修术中取出的金属假体柄研究提示,柄的松动主要发生在骨水泥与骨髓腔内壁界面而非骨水泥与假体柄界面。骨水泥-骨界面的力学强度主要取决于界面区域骨形态和骨水泥与骨之间的交锁程度,影像学、力学测试、有限元分析等研究显示骨水泥-骨界面的扭转力、剪切力、混合力及蠕变-疲劳应力条件下强度变化等微力学变化与假体松动相关。界面反复微动引起的摩损碎屑颗粒和离解产生的微小颗粒物质,引起一系列免疫反应及机体自身对这些颗粒的反应,促使假体周围发生骨溶解,加剧假体松动。该文就骨水泥-骨界面微力学变化特点及假体松动机制作一综述。     

柄的形态对近端股骨应力的影响——Langhans M, Hofmann D, Ecke H et al.

非骨水泥型股骨假体柄的设计和长度差别很大。柄的直径和材料也不相同。设计者因此也提出了不同的固定理论。骨不是一个静态的结构而是处在一种持续重建过程中。应力增加时通过新骨生长增加应力耐受性。当应力大于骨修复能力时骨溶解开始。初始固定要求尽量紧固,以避免假体在应力下松动。但当比较不同股骨假体形状对固定点影响时,要考虑对股骨的应力。下面研究分述不同的股骨假体对股骨皮质应力的影响。 1 材料和方法 在这个实验中,9种非骨水泥型股骨假     

全髋关节置换前后股骨应力变化的有限元分析

目的:研究Chamley Elite骨水泥型和Summit近端多孔非骨水泥型股骨假体置换后股骨总体应力以及假体周围骨质区应力分布的变化。方法:根据Charnley Elite骨水泥柄和Summit非骨水泥柄假体形态建立三维有限元模型，并加载关节合力以及相关肌肉的肌力负荷，分析假体植入前后股骨总体应力模式并对股骨近端假体周围区域骨质应力分布进行分区量化研究。结果:两种假体植入后没有改变股骨总体的应力模式，应力峰值区域均位于全长股骨的中下段，但股骨应力峰值有所下降。股骨近端假体周围骨质等效应力水平出现了显著下降，下降最严重的区域为近段内侧象限即股骨距区，应力遮挡率分别达90．8％和95．3％；向假体远端应力水平逐渐增大，直至假体远段和末段水平应力值逐渐恢复并接近生理水平。就该两种不同固定方式的假体比较而言，引起的应力遮挡区域分布基本一致，应力下降程度Summit近端多孔非骨水泥型假体要高于Charnley Elite骨水泥型假体。结论:两种假体植入后均在股骨近端形成显著的应力遮挡，假体周围骨质应力大小和分布的改变是引起术后骨量丢失和假体松动的原因之一，也是术后股骨骨折发生的类型以术后肢体疼痛发生的力学基础。两种固定方式的假体均需通过进一步改进以减少应力遮挡。     

基于偏髓分型应用骨水泥型长短柄假体置换治疗高龄偏髓Ⅰ型粗隆间骨折的有限元分析（英文）

[目的]探讨高龄偏髓Ⅰ型粗隆间骨折行骨水泥型股骨假体置换术后的股骨应力分布,并对比分析长、短假体柄置换后的应力分布差异。[方法]利用螺旋CT对志愿者的右侧股骨进行断层扫描获取图像数据,将图像数据经Mimics软件和建模软件处理后重建股骨三维模型。在此基础上,建立偏髓Ⅰ型粗隆间骨折长、短柄股骨假体及骨水泥套的三维实体模型,最后利用有限元分析软件建立长、短柄股骨假体治疗粗隆间骨折的三维有限元模型,并对该模型进行生物力学分析。[结果]长、短柄假体置换后股骨的应力分布没有发生明显改变,依然是由近端向远端逐渐增加,至内外侧中下1/3交界处达到峰值,再向末端又减小。短柄假体骨水泥-假体柄界面在末端内外侧虽形成应力集中区,且外侧峰值为15.3 MPa,但未超过骨水泥疲劳强度;而长柄假体在骨水泥-假体柄界面远端内外侧及内侧中段形成应力集中区,其峰值也均低于骨水泥疲劳强度。骨水泥重建的股骨距部位未见明显的应力集中区。[结论]骨水泥型长、短柄假体置换治疗高龄偏髓Ⅰ型粗隆间骨折不会引起股骨应力分布的明显改变。长柄假体的松动概率与短柄假体基本相当,但后者由于手术时间短、创伤小、并发症少,可能更适合治疗高龄偏髓Ⅰ型粗隆间骨折。     

骨水泥型长短柄假体置换治疗高龄粉碎性转子间骨折的三维有限元对比分析

目的 探讨高龄粉碎性转子间骨折行骨水泥型股骨假体置换术后的股骨应力分布,并对比分析长、短假体柄置换后的应力分布差异.方法 利用螺旋CT对志愿者的左侧股骨进行断层扫描获取图像数据,将图像数据经Mimics软件和Unigraphics建模软件处理后重建股骨三维模型.在此基础上,建立粉碎性转子间骨折、长、短柄股骨假体及骨水泥套的三维实体模型,最后利用有限元分析软件ABAQUS6.5建立长、短柄股骨假体治疗粉碎性转子间骨折的三维有限元模型,并对该模型进行生物力学分析.结果 长、短柄假体置换后股骨的应力分布没有发生明显改变,依然是由近端向远端逐渐增加,至内外侧中下1/3交界处达到峰值,再向末端又减小.短柄假体骨水泥-假体柄界面在未端内外侧形成应力集中区,且外侧峰值达21.3 MPa,超过了骨水泥疲劳强度;而长柄假体在骨水泥-假体柄界面远端内外侧及内侧中段形成应力集中区,但其峰值均低于骨水泥疲劳强度.骨水泥重建的股骨距部位未见明显的应力集中区.结论 骨水泥型长、短柄假体置换治疗高龄粉碎性转子间骨折不会引起股骨应力分布的明显改变.长柄假体的松动概率小于短柄假体,前者可能更适合治疗高龄粉碎性转子间骨折.     

节段性骨缺损的假体置换术——两种多孔表面假体皮质外固定作用的比较

重要长骨因骨肿瘤或严重创伤而作节段切除后,如何恢复其连续性是骨科临床最棘手的问题之一。通常用自体或异体骨移植或用定制的假体并以骨水泥固定,但可并发骨水泥失效、假体柄折断、界面松动和应力遮挡性骨质疏松。为此,人们应用多孔表面假体以避免这些问题。但假体柄如同时具有多孔表面则其疲劳强度将下降,且无骨水泥作初始固定而无法保证骨长入和达     

柄的形态对近端股骨应力的影响

非骨水泥型股骨假体柄的设计和长度差别很大.柄的直径和材料也不相同.设计者因此也提出了不同的固定理论.骨不是一个静态的结构而是处在一种持续重建过程中.应力增加时通过新骨生长增加应力耐受性.当应力大于骨修复能力时骨溶解开始.初始固定要求尽量紧固,以避免假体在应力下松动.但当比较不同股骨假体形状对固定点影响时,要考虑对股骨的应力.下面研究分述不同的股骨假体对股骨皮质应力的影响.     

股骨假体柄一丙烯酸骨水泥界面剪切应力的研究进展

无菌性松动是骨水泥型全髋关节置换术后股骨柄翻修最重要的原因之一.松动可发生在股骨-骨水泥界面或假体柄-骨水泥界面.假体柄-骨水泥界面松动是骨水泥型假体初始和远期稳定性下降的主要原[1].假体柄-骨水泥界面主要受剪切应力的作用而破坏[2].界面剪切应力(interfacial shear stress)计算公式[3];     

肿瘤切除假体置换术后皮质外骨桥形成

目前 ,关节周围肿瘤切除、假体置换术后无菌性松动仍然是一个比较棘手的问题。为减少这种无菌性松动的发生率 ,一种新的复合、节段性假体应运而生。这种假体柄的肩部表面以多孔覆盖 ,以利皮质外骨桥形成及骨的长入。其设计理念是基于骨水泥固定提供即刻的稳定性 ,而髓腔外的小孔设计延长了假体 ,并且允许骨桥的形成及骨向小孔内长入。皮质外骨桥的形成及其防止假体松动的作用已被多项实验证明。从有限元分析来看 ,皮质外骨桥形成及假体内骨的长入减少了柄的应力及骨水泥的作用力。因此这种假体被认为因应力的分散而能获得更好的远期效果。本…     

人工股骨头置换术后假体柄断裂的光弹性研究

关节假体柄部断裂在股骨头置换术后并非少见。本实验采用光弹性技术研究模拟人工股骨头假体应力分布，分析人工股骨头假体柄断裂的因素。通过实验研究及８例（９个部位）人工股骨头置换术后假体柄断裂的临床观察，确定其致柄断裂的因素为：①骨水泥的填充和股骨距的截取对假体的应力分布有直接影响；②人工股骨头假体装置不当，如假体内翻或外翻畸形位，均能形成柄部应力集中；③人工股骨头假体一旦出现松动，原装置的假体与股骨上段应力分布发生改变，易导致柄部疲劳断裂。研究资料与临床观察结果为人工股骨头置换术后预防假体柄断裂提供了科学依据     

Factors affecting cement strains near the tip of a cemented femoral component

A generic three-dimensional finite-element model of the upper half of the femur containing a cemented femoral stem of a total hip arthroplasty was developed to study those factors influencing cement strains near the tip of a cemented femoral component. This generic model was verified through another three-dimensional finite-element model that had been created based on the precise geometry of a cadaver femur implanted with a contemporary cemented femoral component. This cadaveric femoral reconstruction had been created with strain gauges embedded in the cement mantle and was then loaded under conditions simulating single leg stance and stairclimbing. By use of the cement strains measured experimentally in the cadaver femur, and comparison of them with those obtained from the finite-element model of that cadaver femur, it was possible to establish proper material properties, boundary conditions, and loading conditions for the generic model. The generic model was then modified parametrically to determine those factors that influence the strains occurring within the cement mantle near the tip of a cemented femoral component. These models suggest that the single factor that most adversely influenced peak strains at or near the tip of the prosthesis was a thin cement mantle. This effect was present both when the cement mantle was reduced in thickness and when a similar effect occurred by virtue of a varus or valgus placement of the stem. Factors that decreased the peak cement strains near the tip of the femoral stem included a more flexible stem and thicker cement mantles. This effect of a more flexible stem could be obtained by changing the modulus of the metal implant, by uniformly reducing the thickness of the stem, or by tapering the stem within the same bone geometry. Thicker cement mantles reduced both the axial and the shear strains occurring at the tip of the prosthesis. The presence or absence of a hole in the tip of the prosthesis per se, as for a centralizer, had no significant effect on the peak cement strains seen around the tip of the prosthesis; however, truncating the tip of the prosthesis from a hemisphere to a flat profile, which resulted in a sharp corner at the tip of the prosthesis, produced a 35% increase in cement strains at the tip as a result of a stress concentration effect. Thus, the common way of modifying the tip to have a hole for a centralizer, which involved truncating the tip, increased the cement strains occurring near the tip of the prosthesis.     

What must be a well-cemented prosthesis?

To avoid cement stem debonding of the Charnley prosthesis, I modified in 1972 the geometry of this prosthesis to subject the cement only to stresses it can resist and protect it against harmful stresses. This was done by giving the stem such a shape that the stresses within the cement would be decreased to a level consistent with its physical properties. On the acetabular size, there has been no modification of the Charnley acetabular component, I only specified how to prepare the acetabulum and implant the socket in order to make it in mechanical harmony with the bone cavity.     

Clinical and radiological results of individual hip stems of the type Adaptiva(R) without cement

AIM: Long-term anchorage of foreign material in vital bone has proven to be the main problem in hip arthroplasty. Bone cement, a material for filling and fitting, allows an excellent solution for older people. Many failures have been blamed on the use of polymethylmethacrylate in younger patients. In our opinion, modelling a stem to the individual anatomic needs of younger patients and to implant it without cement but with a stable press-fit is a good way to transmit stress harmoniously from the prosthesis to the bone and to obtain a long-lasting function. This individual hip stem is now available in the third generation under the name Adaptiva(R). We would like to present our first results. METHOD: Between October 1993 and September 1995 150 individual hip prosthesis of the Adaptiva(R) type have been implanted. In the average the patients were 53,2 years old. The average time of follow-up was 19.9 (12 to 44) months. RESULTS: The Merle d'Aubigné score showed excellent absolute and relative results for pain, mobility and ability to walk. No aseptic loosening of the stem occurred. CONCLUSION: Our early results are promising, but we have to wait for the long-term results, which are part of a current study.     

Effects of distal cement voids on cement stress in total hip arthroplasty

The purpose of this study was to determine whether voids in the distal cement mantle created during total hip arthroplasty increase cement stress at the distal tip of the femoral component. Using a three-dimensional finite element model of an idealized, cylindrical femoral shaft with implanted prosthesis, peak von Mises stress in the cement mantle was evaluated for five different air-bubble configurations and two cement mantle thicknesses, 2 mm and 5 mm. Results indicated that voids in the cement mantle increased peak cement stress at the medial tip of the prosthesis by 2% to 57%, with greater increases in stress being evident with larger bubble sizes. On the average, peak stresses were 53% greater in the models with the thinner cement mantle. Clinicians are encouraged to use a thicker cement mantle and to avoid bubble formation during total hip arthroplasty.     

In vivo surface wear mechanisms of femoral components of cemented total hip arthroplasties: the influence of wear mechanism on clinical outcome

The appearance and mechanism of femoral stem wear was studied in 172 retrieved femoral components, of which 74 stems had been stable in vivo. Macroscopic, microscopic, and nano-level scales of examination were used. Loss of stem surface in response to micromotion (wear) was found to affect 93% of stems. However, changes were frequently difficult to see with the naked eye, and in 19% of cases they would have been missed completely without the use of light microscopy. The surface finish of the prosthesis determined the mechanism of stem wear. Matte surfaces showed typical abrasive processes that also damage the cement, releasing particulate debris from the cement and metal surfaces. This may destabilize the stem within the cement. Polished stems showed a typical fretting appearance with retention of debris on the stem surface and without significant damage to the cement. These differences in wear mechanism between matte and polished stems have significant effects on stem function.     

Stress distribution in the ulna following a hinged elbow arthroplasty. A finite element analysis

The failure rates for total elbow arthroplasty, in comparison to those for hip arthroplasty, are quite high, and a precise understanding of the underlying causes still remains elusive. The presence of abnormal stresses is a known factor that accelerates loosening of hip and knee arthroplasties. Although a large number of biomechanical studies have led to a better understanding of elbow joint kinetics, very little is known about the stress distribution in this joint. The implantation of a Coonrad humeral component increases stresses in the bone and cement adjacent to the stem tip and hinge regions. An analysis of implanted ulnar stresses and a comparison of those stresses to implanted humeral stresses would improve our understanding of hinged elbow arthroplasty. For this reason, the distribution of mechanical stresses in the ulna are investigated in this study. Using a specially developed casting and sectioning technique, three-dimensional finite element meshes were obtained from an intact human cadaver ulna and an ulna fitted with a Coonrad prosthesis. The material properties were derived from values presented in the literature. Stress distributions in response to axial compression, axial torque, and anteroposterior (AP) force were computed. The cancellous bone and cement regions adjacent to the stem tip of the prosthesis exhibited higher stresses than those in the same regions of the intact case. The higher stresses in the ulna with an implanted prosthesis, as compared to the intact model, might initiate loosening or failure of the prosthesis. The stresses in the cortical bone region adjacent to the prosthesis head were decreased. This is consistent with the clinical observations of bone atrophy following total elbow arthroplasty.(ABSTRACT TRUNCATED AT 250 WORDS)     

A Mechanical Analysis of Femoral Resurfacing Implantation for Osteonecrosis of the Femoral Head

Hip resurfacing is becoming a popular procedure for treating osteonecrosis of the femoral head. However, the biomechanical changes that occur after femoral resurfacing have not been fully investigated with respect to the individual extent of the necrosis. In this study, we evaluated biomechanical changes at various extents of necrosis and implant alignments using the finite element analysis method. We established 3 patterns of necrosis by depth from the surface of femoral head and 5 stem angles. For these models, we evaluated biomechanical changes associated with the extent of necrosis and the stem alignment. Our results indicate that stress distribution near the bone-cement interface increased with expansion of the necrosis. The maximum stress on the prosthesis was decreased with stem angles ranging from 130° to140°. The peak stress of cement increased as the stem angle became varus. This study indicates that resurfacing arthroplasty will have adverse biomechanical effects when there is a large extent of osteonecrosis and excessive varus or valgus implantation of the prosthesis.     

Preventing distal voids during cementation of the femoral component in total hip arthroplasty

Cement voids have been noted in close approximation to the unfilled hole in the distal end of the femoral prosthesis. These cement voids result from the displacement of cement by the expansion of air trapped in the distal prosthesis. Voids in the distal cement have been shown to lead to an increased incidence of cement failures. This potentially deleterious situation can easily be avoided by plugging the hole in the distal stem. This may be accomplished three ways: using a centralizer, using the plastic plug supplied with the prosthesis, or filling the hole with cement prior to implanting the prosthesis.     

Initial effect of collarless stem stiffness on femoral bone strain

Stress shielding resulting from a stiffness mismatch between bone and femoral prosthesis stems (leading to bone resorption in the proximal femur) is believed to contribute to failure in total hip arthroplasty. In this study, strains were measured under compressive femoral head loads both in the intact femur and after implanting first a collarless steel stem and then a geometrically identical fiber-reinforced polymer composite stem 64% less stiff. Decreasing stem stiffness would be expected increase load transfer from the stem to the proximal medial femur, decreasing the degree of stress shielding. The authors found that proximal medial bone strains were significantly lower with either the steel or composite stem implanted than in the intact case. However, there were no significant differences in strain patterns between the steel and composite stem cases. This apparent insensitivity to prosthesis stiffness may result from factors related to implant geometry and fit.