DEGRADATION IN POLYETHYLENE JOINT COMPONENTS

全关节置换术是一种公认的治疗方法 关节严重受损。然而，存在严重的并发症， 可能会限制完全关节置换的长期成功。其中几个 这些并发症与超高压杆的机械故障有关。 可能受化学物质影响的相对分子质量聚乙烯 聚乙烯的降解。这项研究的目的是 测定聚乙烯中发生的化学降解的程度 全关节置换术中的部件。降解受以下因素的影响 化学环境和其所在的加载历史 聚乙烯在体内暴露。化学性质，如分子 重量和结晶度随注入时间的变化而变化 在密度等物理性质上也会有相应的变化 以及弹性模数等力学性能。对…的依赖 聚乙烯的化学、物理和力学性能 退化和加载历史将通过暴露试件来确定 到模拟体内环境的流体，到循环加载， 以及两者的组合作为时间的函数。体内的变化 在化学和物理性能方面，聚乙烯将 确定为时间和位置的函数(在装载和卸载时 从一项前瞻性研究中检索到的胫骨部件中的 膝盖置换手术。材料的力学性能退化过程 通过执行以下操作来预测取回的胫骨组件 机械性能不同的应力分析序列 如降级和加载历史所指示的 体外实验中化学性能与力学性能的关系 测试。然后将执行参数研究以确定变量 在与几何形状微小变化引起的退化相关的应力中 股骨和胫骨的全膝关节假体。目标将是 确定将加载历史影响降至最低的几何形状 降解，因此提高了聚乙烯的性能 组件，同时为 全膝关节置换手术。

Total joint replacement is an established method of treatment for severely impaired joints. However, significant complications exist which may limit the long-term success of total joint replacements. Several of these complications are associated with mechanical failure of ultra high molecular weight polyethylene, which may be affected by chemical degradation of the polyethylene. The purpose of this research is to determine the extent of chemical degradation occurring in polyethylene components in total joint arthroplasty. The degradation is affected by both the chemical environment and the loading history to which polyethylene is exposed in vivo. Chemical properties such as molecular weight and percent crystallinity are changed with time of implantation and there is an associated change in physical properties such as density and in mechanical properties such as elastic modulus. The dependence of the chemical, physical, and mechanical properties of polyethylene on degradation and loading history will be determined by exposing specimens to a fluid which simulates the in vivo environment, to cyclic loading, and to a combination of both as a function of time. The in vivo changes in the chemical and physical properties of polyethylene will be determined as a function of time and of location (in loaded and unloaded areas) in tibial components retrieved from a prospective study of total knee replacements. The course of degradation of mechanical properties for the retrieved tibial components will be predicted by performing a sequence of stress analyses in which the mechanical properties are varied as dictated by degradation and loading history utilizing the determined relationship between chemical and mechanical properties from the in vitro test. Parametric studies will then be performed to determine variations in stresses associated with degradation due to small changes in geometry of the femoral and tibial total knee components. The goal will be to determine the geometry which minimizes the effects of loading history on degradation and, therefore, improves the performance of polyethylene components while maintaining appropriate kinematic constraints for the total knee replacement.