Lee I Y, Skinner H B, Keyak J H
Rehabilitation R&D, VA Medical Center, San Francisco, California.
J Biomed Mater Res. 1994 Sep;28(9):1055-60. doi: 10.1002/jbm.820280910.
With the resurgence of the use of bone cement in total hip arthroplasty, a renewed interest in techniques or designs that may reduce cement fixation failure has arisen. Analysis of the stresses at the tip of the prosthesis may suggest strategies to reduce loosening. This study analyzed stresses in the cement near the tip of a femoral component as a function of cement thickness, using a three-dimensional finite element model. A section of an idealized circular femoral shaft with implanted prosthesis and cement was modeled with loading conditions representing the stance phase of gait. Increasing cement thickness from 2 to 5 mm by reducing the prosthesis diameter from 15 to 9 mm is predicted to reduce stress significantly in the cement mantle of a femoral implant. Peak tensile stresses are reduced 45%, whereas peak von Mises and shear stresses are reduced 40%. Such a reduction in stress can increase fatigue life by an order of magnitude. Peak interface tensile stresses occur on the medial side at the tip of the prosthesis in a transverse direction, indicating likelihood of failure due to debonding. The shear and tensile stresses predicted by our model greatly exceed the fatigue endurance limit values for both bulk cement and the cement-prosthesis interface, indicating the likelihood of premature fatigue failure, even allowing for considerable uncertainty. These analytical results suggest that the surgeon should adopt a strategy of selecting a prosthesis that permits a 5-mm cement mantle near the tip of the prosthesis.
随着骨水泥在全髋关节置换术中的再度应用，人们对可能减少骨水泥固定失败的技术或设计重新产生了兴趣。对假体尖端应力的分析可能会提出减少松动的策略。本研究使用三维有限元模型，分析了股骨部件尖端附近骨水泥中的应力与骨水泥厚度的函数关系。对一段植入假体和骨水泥的理想化圆形股骨干进行建模，加载条件代表步态的站立期。预计通过将假体直径从15毫米减小到9毫米，使骨水泥厚度从2毫米增加到5毫米，可显著降低股骨植入物骨水泥套中的应力。峰值拉应力降低45%，而峰值冯·米塞斯应力和剪应力降低40%。这种应力降低可使疲劳寿命提高一个数量级。峰值界面拉应力出现在假体尖端内侧的横向，表明由于脱粘而导致失败的可能性。我们模型预测的剪应力和拉应力大大超过了整体骨水泥和骨水泥 - 假体界面的疲劳耐力极限值，表明即使存在相当大的不确定性，也可能出现过早疲劳失效。这些分析结果表明，外科医生应采取一种策略，即选择一种能在假体尖端附近形成5毫米厚骨水泥套的假体。
