Hashemi A., Shirazi-Adl A.
Division of Applied Mechanics, Department of Mechanical Engineering, Ecole Polytechnique, Montréal, Québec, Canada.
Comput Methods Biomech Biomed Engin. 2000;3(3):183-201. doi: 10.1080/10255840008915264.
A three dimensional nonlinear finite element model was developed to investigate tibial fixation designs and friction models (Coulomb's vs nonlinear) in total knee arthroplasty in the immediate postoperative period with no biological attachment. Bi-directional measurement-based nonlinear friction constitutive equations were used for the bone-porous coated implant interface. Friction properties between the polyethylene and femoral components were measured for this study. Linear elastic isotropic but heterogeneous mechanical properties taken from literature were considered for the bone. The Tensile behaviour of polyethylene was measured and subsequently modeled by an elasto-plastic model. Based on the earlier finite element and experimental pull-out studies, pegs and screws were also realistically modeled. The geometry of every component was obtained through measurement. The PCA tibial baseplate with three different configurations was considered; one with three screws, one with one screw and two short inclined porous-coated pegs, and a third one with no fixation for the sake of comparison. The axial load of 2000N was applied through the femoral component on the medial plateau of articular insert. It was found that Coulomb's friction significantly underestimates the relative micromotion at the bone-implant interface. The lowest micromotion and lift-off were found for the design with screws. Relative micromotion and stress transfer at the bone-implant interface depended significantly on the friction model and on the baseplate anchorage configuration. Cortical and cancellous bones carried, respectively, 10-13% and 65-86% of the axial load depending on the fixation configuration used. The remaining portion was transmitted as shear force by screws and pegs. Normal and Mises stresses as well as contact area in the polyethylene insert were nearly independent of the baseplate fixation design. The Maximum Mises stress in the polyethylene exceeded yield and was found 1-2 mm below the contact surface for all designs.
建立了一个三维非线性有限元模型，以研究全膝关节置换术后早期无生物附着情况下的胫骨固定设计和摩擦模型（库仑摩擦模型与非线性摩擦模型）。基于双向测量的非线性摩擦本构方程用于骨-多孔涂层植入物界面。本研究测量了聚乙烯与股骨部件之间的摩擦性能。骨的力学性能采用文献中的线性弹性各向同性但非均匀的特性。测量了聚乙烯的拉伸行为，随后用弹塑性模型进行建模。基于早期的有限元分析和实验拔出研究，对销钉和螺钉也进行了逼真的建模。每个部件的几何形状通过测量获得。考虑了具有三种不同配置的PCA胫骨基板；一种配置有三个螺钉，一种配置有一个螺钉和两个短倾斜多孔涂层销钉，第三种配置为无固定，以便进行比较。通过股骨部件在关节插入物的内侧平台上施加2000N的轴向载荷。结果发现，库仑摩擦显著低估了骨-植入物界面处的相对微动。螺钉设计的微动和抬起最低。骨-植入物界面处的相对微动和应力传递显著取决于摩擦模型和基板锚固配置。根据所使用的固定配置，皮质骨和松质骨分别承受轴向载荷的10%-13%和65%-86%。其余部分由螺钉和销钉作为剪切力传递。聚乙烯插入物中的法向应力、米塞斯应力以及接触面积几乎与基板固定设计无关。所有设计中，聚乙烯中的最大米塞斯应力均超过屈服强度，且在接触表面下方1-2mm处出现。
