Physical Medicine and Rehabilitation Department, Northwestern University, 345 East Superior Street, Chicago, IL, 60611, USA.
Legs + Walking Lab, Shirley Ryan AbilityLab, 355 East Erie, Chicago, IL, 60611, USA.
Biomech Model Mechanobiol. 2019 Dec;18(6):1563-1575. doi: 10.1007/s10237-019-01159-9. Epub 2019 May 8.
Knee articular cartilage is characterized by a complex mechanical behavior, posing a challenge to develop an efficient and precise model. We argue that the cartilage damage, in general, can be traced to the fibril level as a plastic deformation, defined as micro-defects. To investigate these micro-defects, we have developed a detailed finite element model of the entire healthy tibiofemoral joint (TF) including a multiscale constitutive model which considers the structural hierarchies of the articular cartilage. The net model was simulated under physiological loading conditions to predict joint response under 2000 N axial compression and damage initiation under high axial loading (max 7 KN) when the TF joint flexed to 30°. Computed results sufficiently agreed with earlier experimental and numerical studies. Further, initiation and propagation of damage in fibrils were computed at the tibial cartilage located mainly in the superficial and middle layers. Our simulation results also indicated that the stiffer the fibril is (higher cross-link densities), the higher the contact stress required to elicit a fibril yield and the higher the rate of yielding as a function of increased contact stress. To the best of our knowledge, this is the first model that combines macro-continuum joint mechanics and micromechanics at the tissue level. The computational construct presented here serves as a simulation platform to explore the interplay between acute cartilage damage and micromechanics characteristics at the tropocollagen level.
膝关节软骨的机械行为非常复杂，因此开发高效、精确的模型颇具挑战。我们认为，软骨损伤通常可以追溯到纤维水平，这是一种塑性变形，定义为微缺陷。为了研究这些微缺陷，我们开发了一个详细的全膝关节（TF）的有限元模型，包括一个多尺度本构模型，考虑了关节软骨的结构层次。在生理负荷条件下模拟净模型，以预测在 2000N 轴向压缩下的关节反应，以及当 TF 关节弯曲到 30°时，在高轴向加载（最大 7KN）下的损伤起始。计算结果与早期的实验和数值研究充分吻合。此外，在胫骨软骨中计算了位于浅层和中层的纤维中的损伤起始和扩展。我们的模拟结果还表明，纤维越硬（交联密度越高），引起纤维屈服所需的接触应力越高，随着接触应力的增加，屈服率越高。据我们所知，这是第一个将宏观关节力学和组织水平的细观力学相结合的模型。这里提出的计算结构作为一个模拟平台，用于探索急性软骨损伤和原胶原蛋白水平的细观力学特性之间的相互作用。
