Behforootan Sara, Chatzistergos Panagiotis E, Chockalingam Nachiappan, Naemi Roozbeh
Faculty of Health Sciences, Staffordshire University, Stoke-on-Trent, UK.
Faculty of Health Sciences, Staffordshire University, Stoke-on-Trent, UK.
J Mech Behav Biomed Mater. 2017 Apr;68:287-295. doi: 10.1016/j.jmbbm.2017.02.011. Epub 2017 Feb 9.
Pathological conditions such as diabetic foot and plantar heel pain are associated with changes in the mechanical properties of plantar soft tissue. However, the causes and implications of these changes are not yet fully understood. This is mainly because accurate assessment of the mechanical properties of plantar soft tissue in the clinic remains extremely challenging.
To develop a clinically viable non-invasive method of assessing the mechanical properties of the heel pad. Furthermore the effect of non-linear mechanical behaviour of the heel pad on its ability to uniformly distribute foot-ground contact loads in light of the effect of overloading is also investigated.
An automated custom device for ultrasound indentation was developed along with custom algorithms for the automated subject-specific modeling of heel pad. Non-time-dependent and time-dependent material properties were inverse engineered from results from quasi-static indentation and stress relaxation test respectively. The validity of the calculated coefficients was assessed for five healthy participants. The implications of altered mechanical properties on the heel pad's ability to uniformly distribute plantar loading were also investigated in a parametric analysis.
The subject-specific heel pad models with coefficients calculated based on quasi-static indentation and stress relaxation were able to accurately simulate dynamic indentation. Average error in the predicted forces for maximum deformation was only 6.6±4.0%. When the inverse engineered coefficients were used to simulate the first instance of heel strike the error in terms of peak plantar pressure was 27%. The parametric analysis indicated that the heel pad's ability to uniformly distribute plantar loads is influenced both by its overall deformability and by its stress-strain behaviour. When overall deformability stays constant, changes in stress/strain behaviour leading to a more "linear" mechanical behaviour appear to improve the heel pad's ability to uniformly distribute plantar loading.
The developed technique can accurately assess the visco-hyperelastic behaviour of heel pad. It was observed that specific change in stress-strain behaviour can enhance/weaken the heel pad's ability to uniformly distribute plantar loading that will increase/decrease the risk for overloading and trauma.
诸如糖尿病足和足底足跟疼痛等病理状况与足底软组织力学性能的变化相关。然而，这些变化的原因及影响尚未完全明晰。这主要是因为在临床中准确评估足底软组织的力学性能仍极具挑战性。
研发一种临床上可行的无创方法来评估足跟垫的力学性能。此外，鉴于过载的影响，还研究了足跟垫的非线性力学行为对其均匀分布足-地接触载荷能力的影响。
开发了一种用于超声压痕的自动化定制设备以及用于足跟垫自动化特定个体建模的定制算法。分别从准静态压痕和应力松弛试验的结果中反向设计非时间依赖性和时间依赖性材料特性。对五名健康参与者评估了计算系数的有效性。在参数分析中还研究了力学性能改变对足跟垫均匀分布足底负荷能力的影响。
基于准静态压痕和应力松弛计算系数的特定个体足跟垫模型能够准确模拟动态压痕。最大变形时预测力的平均误差仅为6.6±4.0%。当使用反向设计的系数模拟足跟首次着地时，峰值足底压力方面的误差为27%。参数分析表明，足跟垫均匀分布足底负荷的能力受其整体可变形性及其应力-应变行为的影响。当整体可变形性保持恒定时，导致更“线性”力学行为的应力/应变行为变化似乎会提高足跟垫均匀分布足底负荷的能力。
所开发的技术能够准确评估足跟垫的粘弹性超弹性行为。观察到应力-应变行为的特定变化会增强/减弱足跟垫均匀分布足底负荷的能力，这将增加/降低过载和创伤的风险。
