Harold K. Dunn Orthopaedic Research Laboratory, University of Utah School of Medicine, Salt Lake City, UT 84108, USA.
J Biomech. 2013 Apr 5;46(6):1121-7. doi: 10.1016/j.jbiomech.2013.01.012. Epub 2013 Mar 1.
Quantifying cartilage contact stress is paramount to understanding hip osteoarthritis. Discrete element analysis (DEA) is a computationally efficient method to estimate cartilage contact stresses. Previous applications of DEA have underestimated cartilage stresses and yielded unrealistic contact patterns because they assumed constant cartilage thickness and/or concentric joint geometry. The study objectives were to: (1) develop a DEA model of the hip joint with subject-specific bone and cartilage geometry, (2) validate the DEA model by comparing DEA predictions to those of a validated finite element analysis (FEA) model, and (3) verify both the DEA and FEA models with a linear-elastic boundary value problem. Springs representing cartilage in the DEA model were given lengths equivalent to the sum of acetabular and femoral cartilage thickness and gap distance in the FEA model. Material properties and boundary/loading conditions were equivalent. Walking, descending, and ascending stairs were simulated. Solution times for DEA and FEA models were ~7 s and ~65 min, respectively. Irregular, complex contact patterns predicted by DEA were in excellent agreement with FEA. DEA contact areas were 7.5%, 9.7% and 3.7% less than FEA for walking, descending stairs, and ascending stairs, respectively. DEA models predicted higher peak contact stresses (9.8-13.6 MPa) and average contact stresses (3.0-3.7 MPa) than FEA (6.2-9.8 and 2.0-2.5 MPa, respectively). DEA overestimated stresses due to the absence of the Poisson's effect and a direct contact interface between cartilage layers. Nevertheless, DEA predicted realistic contact patterns when subject-specific bone geometry and cartilage thickness were used. This DEA method may have application as an alternative to FEA for pre-operative planning of joint-preserving surgery such as acetabular reorientation during peri-acetabular osteotomy.
量化软骨接触压力对于理解髋关节骨关节炎至关重要。离散元分析（DEA）是一种计算效率高的方法，可用于估计软骨接触压力。先前的 DEA 应用由于假设软骨厚度恒定和/或关节几何形状为同心，从而低估了软骨的压力并产生了不现实的接触模式。本研究的目的是：（1）建立具有个体骨骼和软骨几何形状的髋关节 DEA 模型，（2）通过将 DEA 预测值与验证的有限元分析（FEA）模型的预测值进行比较来验证 DEA 模型，（3）通过线性弹性边值问题验证 DEA 和 FEA 模型。在 DEA 模型中表示软骨的弹簧的长度等效于 FEA 模型中髋臼和股骨软骨厚度以及间隙距离的总和。材料特性和边界/加载条件等效。模拟了行走、下楼梯和上楼梯。DEA 和 FEA 模型的求解时间分别约为 7 秒和 65 分钟。DEA 预测的不规则、复杂的接触模式与 FEA 非常吻合。与 FEA 相比，DEA 的接触面积分别小 7.5%、9.7%和 3.7%，用于行走、下楼梯和上楼梯。DEA 模型预测的峰值接触压力（9.8-13.6 MPa）和平均接触压力（3.0-3.7 MPa）高于 FEA（分别为 6.2-9.8 和 2.0-2.5 MPa）。由于不存在泊松效应和软骨层之间的直接接触界面，DEA 高估了压力。尽管如此，当使用个体骨骼几何形状和软骨厚度时，DEA 预测了现实的接触模式。这种 DEA 方法可能适用于替代 FEA，用于关节保存手术的术前规划，例如在髋臼周围截骨术中进行髋臼重新定向。
