Spears Iain R, Miller-Young Janice E, Waters Mark, Rome Keith
Sport and Exercise Subject Group, James Cook University Hospital, University of Teesside, Middlesbrough, UK.
Med Sci Sports Exerc. 2005 Jun;37(6):1030-6.
High internal stress is considered to be a possible cause of heel-pad problems. External biomechanical measurements are used to attempt to understand the causes of heel pain. However, internal stress cannot be measured experimentally. Therefore, the purpose of this study was to quantify the relationship between magnitude of force, time to peak force, and sole angle with internal stresses in the heel using a finite element model.
Computer tomography (CT) was used to create a nonlinear time-dependent three-dimensional finite element model of the heel pad. The material model was based on previously reported force-displacement data derived from in vitro experiments. Although it was not possible to compare internal calculations of stress with experimental data, good agreement was found for external plantar pressures and strains when compared with in vivo values. Internal stresses and external plantar pressures were then investigated for different forces, loading rates (i.e., time to peak force), and angles of foot inclination in the sagittal plane (i.e., sole angle).
The results of the model indicate that compressive stress is localized in the region inferior to the calcaneal tuberosity. Peak internal compressive stress was greater than external plantar pressure. Increasing the loading rate (i.e., reducing the time to peak force) caused plantar pressure to increase to a greater extent than internal stress. The general levels of stress were higher when the heel was loaded in an inclined position (i.e., greater sole angle).
The finite element technique provides a useful step in bridging the gap between external measures and internal mechanics of the heel pad. A combined kinematic, kinetic, and modeling approach may be required when attempting to identify the biomechanical source of heel pain.
高内应力被认为是足跟垫问题的一个可能原因。外部生物力学测量用于试图理解足跟疼痛的原因。然而，内应力无法通过实验测量。因此，本研究的目的是使用有限元模型量化足跟力的大小、达到峰值力的时间以及鞋底角度与内应力之间的关系。
使用计算机断层扫描（CT）创建足跟垫的非线性时变三维有限元模型。材料模型基于先前报道的源自体外实验的力-位移数据。尽管无法将内部应力计算结果与实验数据进行比较，但与体内值相比，在外部足底压力和应变方面发现了良好的一致性。然后研究了不同力、加载速率（即达到峰值力的时间）以及矢状面内足部倾斜角度（即鞋底角度）下的内应力和外部足底压力。
模型结果表明，压缩应力集中在跟骨结节下方区域。峰值内部压缩应力大于外部足底压力。增加加载速率（即减少达到峰值力的时间）导致足底压力的增加幅度大于内应力。当足跟处于倾斜位置加载时（即鞋底角度更大），应力的总体水平更高。
有限元技术为弥合足跟垫外部测量与内部力学之间的差距提供了有用的一步。在试图确定足跟疼痛的生物力学根源时，可能需要结合运动学、动力学和建模方法。
