Erdemir Ahmet, Viveiros Meredith L, Ulbrecht Jan S, Cavanagh Peter R
Department of Biomedical Engineering, Lerner Research Institute, The Cleveland Clinic Foundation, Cleveland, OH 44195, USA.
J Biomech. 2006;39(7):1279-86. doi: 10.1016/j.jbiomech.2005.03.007.
A numerical-experimental approach has been developed to characterize heel-pad deformation at the material level. Left and right heels of 20 diabetic subjects and 20 nondiabetic subjects matched for age, gender and body mass index were indented using force-controlled ultrasound. Initial tissue thickness and deformation were measured using M-mode ultrasound; indentation forces were recorded simultaneously. An inverse finite-element analysis of the indentation protocol using axisymmetric models adjusted to reflect individual heel thickness was used to extract nonlinear material properties describing the hyperelastic behavior of each heel. Student's t-tests revealed that heel pads of diabetic subjects were not significantly different in initial thickness nor were they stiffer than those from nondiabetic subjects. Another heel-pad model with anatomically realistic surface representations of the calcaneus and soft tissue was developed to estimate peak pressure prediction errors when average rather than individualized material properties were used. Root-mean-square errors of up to 7% were calculated, indicating the importance of subject-specific modeling of the nonlinear elastic behavior of the heel pad. Indentation systems combined with the presented numerical approach can provide this information for further analysis of patient-specific foot pathologies and therapeutic footwear designs.
已开发出一种数值实验方法来表征足跟垫在材料层面的变形情况。使用力控超声对20名糖尿病患者以及20名年龄、性别和体重指数相匹配的非糖尿病患者的左右足跟进行压痕测试。使用M型超声测量初始组织厚度和变形情况；同时记录压痕力。利用轴对称模型对压痕方案进行逆有限元分析，并根据个体足跟厚度进行调整，以提取描述每个足跟超弹性行为的非线性材料特性。学生t检验显示，糖尿病患者的足跟垫初始厚度与非糖尿病患者并无显著差异，且硬度也不比非糖尿病患者的足跟垫大。还开发了另一种具有跟骨和软组织解剖逼真表面表征的足跟垫模型，以估计在使用平均而非个体化材料特性时的峰值压力预测误差。计算得出的均方根误差高达7%，这表明对足跟垫非线性弹性行为进行个体特异性建模的重要性。结合本文提出的数值方法的压痕系统可为进一步分析患者特定的足部病变和治疗性鞋类设计提供此类信息。
