Janssen D, Stolk J, Verdonschot N
Orthopaedic Research Lab, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.
Proc Inst Mech Eng H. 2006 May;220(4):533-9. doi: 10.1243/09544119JEIM61.
Clinical studies have shown that adequate fixation of ceramic cups using bone cement is difficult to achieve. As the cement-ceramic bond strength is low, a satisfactory fixation strength requires a cup design that allows mechanical interlocking, although such a design will probably promote cement cracking and therefore cup loosening in the long term. An investigation has been carried out to establish whether a cemented ceramic cup can be designed in such a way that both a satisfactory initial fixation strength is obtained and cement cracking is reduced to levels found around PE cups functioning well in vivo. By means of finite element analysis, the fatigue loading of three geometrically different cemented acetabular cups, with ceramic and PE material properties, has been simulated, and the severity of the crack patterns produced in the cement has been analysed. Furthermore, the fixation strength has been analysed by simulating a pull-out test prior to and after fatigue testing. All ceramic cups produced much larger amounts of cement damage during fatigue testing than any PE cup, caused by stress concentrations in the cement that were attributable to the high stiffness of the ceramic. Even a completely smooth ceramic cup produced more damage than a sharp-grooved PE cup. Owing to the excessive cement cracking, the fixation strength of the ceramic cups dropped after fatigue loading. It is concluded that cemented ceramic cups have an increased risk of long-term mechanical failure by comparison with PE cups, and that a ceramic cup design that combines sufficient fixation strength with low cement failure may be difficult to achieve.
临床研究表明，使用骨水泥对陶瓷杯进行充分固定很难实现。由于骨水泥与陶瓷的粘结强度较低，要获得令人满意的固定强度，杯体设计需允许机械互锁，不过从长远来看，这种设计可能会促使骨水泥出现裂缝，进而导致杯体松动。已开展一项调查，以确定是否能设计出一种骨水泥固定的陶瓷杯，既能获得令人满意的初始固定强度，又能将骨水泥裂缝减少到在体内正常发挥功能的聚乙烯（PE）杯周围所发现的水平。通过有限元分析，模拟了三种几何形状不同、具有陶瓷和PE材料特性的骨水泥固定髋臼杯的疲劳载荷，并分析了骨水泥中产生的裂纹模式的严重程度。此外，通过模拟疲劳测试前后的拔出试验，分析了固定强度。在疲劳测试期间，所有陶瓷杯产生的骨水泥损伤都比任何PE杯大得多，这是由陶瓷的高刚度导致骨水泥中应力集中造成的。即使是完全光滑的陶瓷杯产生的损伤也比有尖锐凹槽的PE杯更多。由于骨水泥过度开裂，陶瓷杯在疲劳加载后的固定强度下降。结论是，与PE杯相比，骨水泥固定的陶瓷杯长期机械失效的风险增加，且要设计出一种兼具足够固定强度和低骨水泥失效的陶瓷杯可能很难实现。
