Lee I Y, Skinner H B, Keyak J H
Rehabilitation R & D, VA Medical Center, San Francisco.
Iowa Orthop J. 1993;13:155-9.
With the resurgence of the use of bone cement in total hip arthroplasty, a renewed concern 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. Using a three-dimensional finite element model this study analyzed stresses in the bone, cement, and prosthesis near the tip of a femoral component as a function of cement thickness. A section of an idealized circular femoral shaft with implant prosthesis and cement was modeled with loading conditions representing the stance phase of gait. Increasing cement thickness is predicted to significantly reduce stress in the cement mantle of a femoral implant. Tensile stress is reduced by fifty percent while shear stress is reduced at least twelve percent. Peak tensile stresses occur on the medial side at the tip of the prosthesis in a transverse direction, indicating likelihood of failure due to debonding. Local shear stress peaks also occur at the tip. Shear stresses in the cement mantle are in the same range as the tensile stresses and must be considered when analyzing the possible modes of failure. However, the mode of failure in shear is complex, and shear strength of the stem-cement interface is unknown at present.
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关注。对假体尖端应力的分析可能会提示减少松动的策略。本研究使用三维有限元模型，分析了股骨部件尖端附近骨、骨水泥和假体中的应力与骨水泥厚度的函数关系。用代表步态站立期的加载条件，对带有植入假体和骨水泥的理想化圆形股骨干截面进行建模。预计增加骨水泥厚度会显著降低股骨植入物骨水泥壳中的应力。拉应力降低了50%，而剪应力至少降低了12%。横向方向上，假体尖端内侧出现峰值拉应力，表明存在因脱粘而导致失败的可能性。局部剪应力峰值也出现在尖端。骨水泥壳中的剪应力与拉应力处于同一范围，在分析可能的失败模式时必须予以考虑。然而，剪切破坏模式很复杂，目前柄-骨水泥界面的抗剪强度尚不清楚。
