Department of Orthopaedic Surgery, Medical Hospital, Tokyo Medical and Dental University, Tokyo, Japan.
J Arthroplasty. 2017 Dec;32(12):3757-3762. doi: 10.1016/j.arth.2017.07.010. Epub 2017 Jul 15.
The post-cam mechanism in posterior stabilized (PS) prostheses plays an important role in total knee arthroplasty (TKA). The purpose of this study is to clarify the difference of the contact stress on the tibial post between a rounded post-cam design and a squared design during deep knee flexion and at hyperextension using the three-dimensional (3D) finite element models.
We created 2 types of 3D, finite element models of PS prostheses (types A and B), whose surfaces were identical except for the post-cam geometries: type A has a rounded post-cam design, while type B has a squared design. Both types have a similar curved-shape intercondylar notch of the femoral component. Stress distributions, peak contact stresses, and contact areas on the tibial posts at 90°, 120°, and 150° flexion with/without 10° tibial internal rotation and at 10° hyperextension were compared between the 2 models.
Type B demonstrated more concentrated stress distribution compared to type A. The peak contact stresses were similar in both groups during neutral flexion; however, the stresses were much higher in type B during flexion with 10° rotation and at hyperextension. The higher peak contact stresses corresponded to the smaller contact areas in the tibial post.
A rounded post-cam design demonstrated less stress concentration during flexion with rotation and at hyperextension compared with a squared design. The results would be useful for development of implant designs and prediction of the contact stress on the tibial post in PS total knee arthroplasty.
后稳定型（PS）假体中的后置凸轮机构在后膝关节置换术（TKA）中起着重要作用。本研究旨在使用三维（3D）有限元模型，明确在膝关节深度屈曲和过伸时，圆形后置凸轮设计与方形设计的胫骨后柱接触应力的差异。
我们创建了 2 种 PS 假体的 3D 有限元模型（A 型和 B 型），其表面除后置凸轮几何形状外完全相同：A 型具有圆形后置凸轮设计，而 B 型具有方形设计。两种类型均具有类似的股骨组件的弯曲状髁间切迹。比较了 2 种模型在 90°、120°和 150°屈曲时（有无 10°胫骨内旋）以及在 10°过伸时胫骨后柱的应力分布、峰值接触应力和接触面积。
与 A 型相比，B 型显示出更集中的应力分布。在中立屈曲时，2 组的峰值接触应力相似；然而，在旋转和过伸时，B 型的应力要高得多。更高的峰值接触应力对应于胫骨后柱更小的接触面积。
与方形设计相比，圆形后置凸轮设计在旋转和过伸时的屈曲时表现出较小的应力集中。研究结果有助于假体设计的开发和预测 PS 全膝关节置换术中胫骨后柱的接触应力。
