Investigation into the Engagement and Performance of Modular Taper Junctions in Total Hip Replacements

Morse型锥形被纳入全髋关节置换术，以允许使用陶瓷轴承材料。在初次和翻修手术期间，模块化还提供了更高的术中灵活性，以及平衡软组织以恢复自然步态的能力。然而，从单块到模块化设计的转变意味着界面处的流体进入和微运动可能会通过微动腐蚀引起降解。锥连接处的磨损和腐蚀产物与患者中常见的局部不良组织反应相关，表现为疼痛和不稳定。最近的一项研究强调了头颈部微动腐蚀的影响。4581例患者中有33例因头颈连接处产生的金属碎屑不良反应而需要翻修金属对聚合物置换。莫尔斯锥度最初设计用于快速更换铣床中的钻头和切削工具等机器部件，而不会影响扭矩传递。锥形表面设计为高度贴合、光滑、坚硬、长且具有轻微锥度。另一方面，股骨头-股骨柄锥度短得多，锥度率高得多（即锥度角越大，锥度越短），通常呈现螺纹光洁度，并呈现一定程度的角度不匹配，以形成特定的接触区域。研究发现，锥度设计影响微动腐蚀量。这已经在变化中看到，例如：材料耦合、机械载荷、界面的表面纹理、标称接触面积、任何应力集中的存在和冲击条件。这些锥形设计变化中的许多影响两个配合锥形接口的接合。之前，几何形状已被用于定量评价宏观尺度的符合性，最多使用三个参数，仅提供对锥体接合的有限了解。一些研究已经调查了表面形貌以评估微观尺度上的接合，忽略了几何形状。该项目的目的是评估由于几何形状和局部偏差导致的锥体接合和性能，其目标分为以下高级目标：-开发测量和分析技术，允许使用精密工程测量设备（如圆度仪和坐标测量机）适当表征锥体界面。- 评估市售组配式股骨头和股骨柄系统在制造商之间和每个制造商内部的差异。确定这些变化如何影响股骨头和股骨柄之间的接合。最后，确定这些锥度变化如何影响股骨头股骨柄系统在锥度力学、缝隙腐蚀敏感性和摩擦腐蚀方面的性能。该项目将更好地了解如何最大限度地减少各种市售全髋关节置换术中每个股骨头和股骨柄对之间医疗器械锥度界面处的微动腐蚀。

Morse-type tapers were incorporated into total hip replacements to allow the use of a ceramic bearing material. Modularity also offers increased intra-operative flexibility during primary and revision surgery and, the ability to balance soft tissues in order restore the natural gait. However, moving from a mono-block to a modular design has meant fluid ingress and micro-motion at the interface can cause degradation via fretting-corrosion. Wear and corrosion products at the taper junction are associated with adverse local tissue reactions commonly presented in patients as pain followed by instability. The effect of fretting corrosion at the head-neck was highlighted in a recent study. Thirty-three (of 4581) patients required revision of a metal-on-polymer replacement due to adverse reaction to metal debris produced as the head-neck junction.Morse tapers were originally designed to allow machine parts such as drill bits and cutting tools in milling machines to be changed quickly without compromising torque transmission. The conical surfaces are designed to be highly conforming, smooth, hard, long and with a slight taper. Head-stem tapers on the other hand are much shorter with a much higher taper rate (i.e. shorter with a greater taper angle), often presenting a threaded finish and present a level of angular mismatch in order to create specific contact regions.Studies have investigated and found that the taper design influences the amount of fretting-corrosion. This has been seen in variations such as: the material couple, mechanical loading, surface texture of the interface, nominal contact area, presence of any stress concentrations and, impaction conditions. Many of these taper deign variations influence the engagement of the two mating taper interfaces. Previously, the geometrical form has been used to quantitatively evaluate macro-scale conformity using a maximum of three parameters providing only a limited insight into taper engagement. Some studies have investigated the surface topography to assess engagement on the micro-scale, neglecting the geometrical form. This project's aim is to assess taper engagement and performance due to geometrical form and local deviations.The aim has been divided into the following high level objectives:- Develop measurement and analysis techniques that allows taper interfaces to be appropriately characterised using precision engineering measurement devices such as Roundness and Coordinate Measurement Machines. - Assess how commercially available modular head and stem systems vary between manufactures and within each manufacturer.- Determine how these variations effect engagement between a head and a stem couple.- Finally, determine how these taper variations affect the performance of head stem systems in terms of taper mechanics, susceptibility to crevice corrosion and tribo-corrosion .This project will provide a better understanding of how fretting corrosion at the taper interface of medical devices can be minimised between each head and stem couple across a range of commercially available total hip replacements.