Petre Marc, Erdemir Ahmet, Panoskaltsis Vassilis P, Spirka Thomas A, Cavanagh Peter R
Division of Anesthesiology and Critical Care Medicine,Cleveland Clinic, Cleveland, OH 44195, USA.
J Biomech Eng. 2013 Jun;135(6):61001-12. doi: 10.1115/1.4023695.
Accurate prediction of plantar shear stress and internal stress in the soft tissue layers of the foot using finite element models would provide valuable insight into the mechanical etiology of neuropathic foot ulcers. Accurate prediction of the internal stress distribution using finite element models requires that realistic descriptions of the material properties of the soft tissues are incorporated into the model. Our investigation focused on the creation of a novel three-dimensional (3D) finite element model of the forefoot with multiple soft tissue layers (skin, fat pad, and muscle) and the development of an inverse finite element procedure that would allow for the optimization of the nonlinear elastic coefficients used to define the material properties of the skin muscle and fat pad tissue layers of the forefoot based on a Ogden hyperelastic constitutive model. Optimization was achieved by comparing deformations predicted by finite element models to those measured during an experiment in which magnetic resonance imaging (MRI) images were acquired while the plantar surface forefoot was compressed. The optimization procedure was performed for both a model incorporating all three soft tissue layers and one in which all soft tissue layers were modeled as a single layer. The results indicated that the inclusion of multiple tissue layers affected the deformation and stresses predicted by the model. Sensitivity analysis performed on the optimized coefficients indicated that small changes in the coefficient values (±10%) can have rather large impacts on the predicted nominal strain (differences up to 14%) in a given tissue layer.
使用有限元模型准确预测足底剪切应力以及足部软组织层的内部应力，将为神经性足部溃疡的力学病因提供有价值的见解。使用有限元模型准确预测内部应力分布，需要将软组织材料特性的真实描述纳入模型。我们的研究重点是创建一个具有多个软组织层（皮肤、脂肪垫和肌肉）的前足新型三维（3D）有限元模型，以及开发一种逆有限元程序，该程序将允许基于Ogden超弹性本构模型优化用于定义前足皮肤、肌肉和脂肪垫组织层材料特性的非线性弹性系数。通过将有限元模型预测的变形与在实验中测量的变形进行比较来实现优化，该实验在压缩前足底表面时采集磁共振成像（MRI）图像。对包含所有三个软组织层的模型和将所有软组织层建模为单层的模型都进行了优化程序。结果表明，包含多个组织层会影响模型预测的变形和应力。对优化系数进行的敏感性分析表明，系数值的小变化（±10%）可能对给定组织层中预测的名义应变产生相当大的影响（差异高达14%）。
