Department of Mechanical and Manufacturing Engineering, University of Calgary, 2500 University Drive, N.W., Calgary, Alberta, Canada T2N 1N4.
Med Eng Phys. 2013 Nov;35(11):1591-8. doi: 10.1016/j.medengphy.2013.05.005. Epub 2013 Jun 10.
The material properties of articular cartilage are depth-dependent, i.e. they differ in the superficial, middle and deep zones. The role of this depth-dependent material inhomogeneity in the poromechanical response of the knee joint has not been investigated with patient-specific joint modeling. In the present study, the depth-dependent and site-specific material properties were incorporated in an anatomically accurate knee model that consisted of the distal femur, femoral cartilage, menisci, tibial cartilage and proximal tibia. The collagen fibers, proteoglycan matrix and fluid in articular cartilage and menisci were considered as distinct constituents. The fluid pressurization in the knee was determined with finite element analysis. The results demonstrated the influences of the depth-dependent inhomogeneity on the fluid pressurization, compressive stress, first principal stress and strain along the tissue depth. The depth-dependent inhomogeneity enhanced the fluid support to loading in the superficial zone by raising the fluid pressure and lowering the compressive effective stress at the same time. The depth-dependence also reduced the tensile stress and strain at the cartilage-bone interface. The present 3D modeling revealed a complex fluid pressurization and 3D stresses that depended on the mechanical contact and relaxation time, which could not be predicted by existing 2D models from the literature. The greatest fluid pressure was observed in the medial condyle, regardless of the depth-dependent inhomogeneity. The results indicated the roles of the tissue inhomogeneity in reducing deep tissue fractures, protecting the superficial tissue from excessive compressive stress and improving the lubrication in the joint.
关节软骨的材料特性具有深度依赖性，即它们在表层、中层和深层区域存在差异。这种深度依赖性的材料不均匀性在膝关节的压渗响应中尚未通过特定于患者的关节建模进行研究。在本研究中，将深度依赖性和特定于部位的材料特性纳入由远端股骨、股骨软骨、半月板、胫骨软骨和胫骨近端组成的解剖学精确膝关节模型中。关节软骨和半月板中的胶原纤维、蛋白聚糖基质和流体被视为不同的组成部分。使用有限元分析确定膝关节中的流体加压情况。结果表明，深度依赖性不均匀性对流体加压、压缩应力、第一主应力和沿组织深度的应变的影响。深度依赖性不均匀性通过提高流体压力和同时降低压缩有效应力来增强对浅层加载的流体支撑。深度依赖性还降低了软骨-骨界面处的拉伸应力和应变。本 3D 建模揭示了一种复杂的流体加压和 3D 应力，这取决于机械接触和松弛时间，这是现有文献中的二维模型无法预测的。无论深度依赖性不均匀性如何，最大的流体压力都出现在内侧髁。结果表明组织不均匀性在减少深层组织骨折、保护浅层组织免受过度压缩应力以及改善关节润滑方面的作用。
