Kurtz S M, Ochoa J A, White C V, Srivastav S, Cournoyer J
Failure Analysis Associates, Inc., Menlo Park, CA 94025, USA.
J Biomech. 1998 May;31(5):431-7. doi: 10.1016/s0021-9290(98)00030-x.
Nonconformity between the polyethylene liner and the metal shell may exist in modular acetabular components by design, due to manufacturing tolerances, or from locking mechanisms that attach the polyethylene liner to the metal shell. Relative motion at the liner/shell interface has been associated with backside wear, which may contribute to osteolysis which has been clinically observed near screw holes. The purpose of this study was to investigate the effect of nonconformity and locking restraints on the liner/shell relative motion and load transfer mechanisms in a commercially available, metal-backed acetabular component with a polar fenestration. The finite element method was used to explore the hypothesis that backside nonconformity and locking restraints play important roles in long-term surface damage mechanisms that are unique to modular components, such as backside wear and liner extrusion through screw holes. The three-body quasi-static contact problem was solved using a commercially available explicit finite element code, which modeled contact between the femoral head, polyethylene liner, and the metal shell. Four sets of liner boundary conditions were investigated: no restraints, rim restraints, equatorial restraints, and both rim and equatorial restraints. The finite element model with a conforming shell predicted between 8.5 and 12.8 microm of incremental extrusion of the polyethylene through the polar fenestration, consistent with in vitro experiments of the same design under identical loading conditions. Furthermore, idealized rim and/or equatorial liner restraints were found to share up to 71% of the load across the liner/shell interface. Consequently, the results of this study demonstrate that backside nonconformity and locking restraints substantially influence backside relative motion as well as load transfer at the liner/shell interface.
由于制造公差或用于将聚乙烯内衬固定到金属外壳的锁定机制，模块化髋臼组件中聚乙烯内衬与金属外壳之间可能存在设计上的不一致。内衬/外壳界面处的相对运动与背面磨损有关，这可能导致骨溶解，临床上已在螺钉孔附近观察到这种情况。本研究的目的是调查在一种市售的、带有极孔开窗的金属背衬髋臼组件中，不一致性和锁定约束对内衬/外壳相对运动及载荷传递机制的影响。采用有限元方法来探究以下假设：背面不一致性和锁定约束在模块化组件特有的长期表面损伤机制中起重要作用，如背面磨损和内衬通过螺钉孔挤出。使用商用显式有限元代码求解三体准静态接触问题，该代码对股骨头、聚乙烯内衬和金属外壳之间的接触进行了建模。研究了四组内衬边界条件：无约束、边缘约束、赤道约束以及边缘和赤道均有约束。具有贴合外壳的有限元模型预测，聚乙烯通过极孔开窗的增量挤出量在8.5至12.8微米之间，这与相同设计在相同加载条件下的体外实验结果一致。此外，发现理想化的边缘和/或赤道内衬约束可分担内衬/外壳界面处高达71%的载荷。因此，本研究结果表明，背面不一致性和锁定约束会显著影响背面相对运动以及内衬/外壳界面处的载荷传递。
