Shepard M F, Lieberman J R, Kabo J M
Department of Orthopaedic Surgery, UCLA School of Medicine, Los Angeles, California, USA.
J Arthroplasty. 1999 Oct;14(7):860-6. doi: 10.1016/s0883-5403(99)90038-4.
The generation of debris from the wear of ultra-high-molecular weight polyethylene (UHMWPE) is a well-recognized factor in the development of osteolysis and the long-term failure of total joint arthroplasties. Wear between the articulation of the femoral head and the polyethylene has been recognized for many years, but more recently, both retrieval and in vitro studies have demonstrated that convex surface wear or backside wear also occurs and may be of significance. Currently, modular acetabular components are being designed with polished surfaces, fewer screw holes, various polyethylene locking mechanisms, and stiffer metal alloys in an attempt to reduce backside wear. The purpose of this study was to determine if differences existed in UHMWPE wear based on the metal alloy used and the surface finish in modular acetabular components. Sixteen components in 4 groups were subjected to 10 million gait cycles using an in vitro joint simulator. All components used 28-mm cobalt chrome femoral heads on cobalt chrome tapered stems. The 4 groups differed only in the type of metal backing and type of interior finished surface: polished cobalt chrome, unpolished cobalt chrome, polished titanium, and unpolished titanium. UHMWPE changes were examined in terms of articular (concave) surface wear, backside (convex) surface wear, and frictional torque. The overall linear and volumetric wear rates were 1.05 mm/10 million cycles and 325 mm3/10 million cycles. No significant differences in linear and volumetric wear rates were detected between the cobalt chrome and titanium acetabular components. Surface finish did not influence wear rates. In terms of backside wear, all specimens in the 4 groups demonstrated total loss of all sputtered gold with the exception of those areas extruded through the screw holes. Extrusion through the screw holes was on the order of 0.0004 inch for all groups, and no significant difference was seen among the groups for this parameter. The measurements of articular frictional torque demonstrated a significant difference among the polished and unpolished cobalt chrome components (17.3 N x m vs 11.5 N x m; P = .0039, 2-way analysis of variance, Student's Newman Keuls method). Some designs in modular acetabular components have favored stiffer alloys, such as cobalt chrome, with polished concave surfaces to decrease wear on both the concave and the convex surfaces. In this study, there was no significant difference in wear rates noted between cobalt chrome and titanium acetabular components, and polishing of the components had no appreciable affect in reducing backside wear.
超高分子量聚乙烯（UHMWPE）磨损产生的碎屑是骨溶解发展和全关节置换长期失败的一个公认因素。股骨头与聚乙烯关节面之间的磨损已被认识多年，但最近，取出研究和体外研究均表明，凸面磨损或背面磨损也会发生，且可能具有重要意义。目前，模块化髋臼组件的设计采用了抛光表面、更少的螺孔、各种聚乙烯锁定机制以及更硬的金属合金，以试图减少背面磨损。本研究的目的是确定基于模块化髋臼组件中使用的金属合金和表面光洁度，UHMWPE磨损是否存在差异。使用体外关节模拟器对4组中的16个组件进行1000万次步态循环测试。所有组件均在钴铬锥形柄上使用28毫米钴铬股骨头。4组之间的差异仅在于金属背衬类型和内部加工表面类型：抛光钴铬、未抛光钴铬、抛光钛和未抛光钛。从关节（凹面）表面磨损、背面（凸面）表面磨损和摩擦扭矩方面检查UHMWPE的变化。总体线性磨损率和体积磨损率分别为1.05毫米/1000万次循环和325立方毫米/1000万次循环。钴铬和钛髋臼组件之间未检测到线性磨损率和体积磨损率的显著差异。表面光洁度不影响磨损率。就背面磨损而言，4组中的所有标本除了通过螺孔挤出的区域外，所有溅射金均完全磨损。所有组通过螺孔的挤出量约为0.0004英寸，该参数在各组之间未观察到显著差异。关节摩擦扭矩的测量表明，抛光和未抛光的钴铬组件之间存在显著差异（17.3牛·米对11.5牛·米；P = 0.0039，双向方差分析，Student-Newman-Keuls法）。模块化髋臼组件中的一些设计倾向于使用更硬的合金，如钴铬，并采用抛光凹面，以减少凹面和凸面的磨损。在本研究中，钴铬和钛髋臼组件之间的磨损率没有显著差异，组件的抛光对减少背面磨损没有明显影响。
