Yarnitzky G, Yizhar Z, Gefen A
Department of Biomedical Engineering, Faculty of Engineering, Tel Aviv University, Israel.
J Biomech. 2006;39(14):2673-89. doi: 10.1016/j.jbiomech.2005.08.021. Epub 2005 Oct 5.
No technology is presently available to provide real-time information on internal deformations and stresses in plantar soft tissues of individuals during evaluation of the gait pattern. Because internal deformations and stresses in the plantar pad are critical factors in foot injuries such as diabetic foot ulceration, this severely limits evaluation of patients. To allow such real-time subject-specific analysis, we developed a hierarchal modeling system which integrates a two-dimensional gross structural model of the foot (high-order model) with local finite element (FE) models of the plantar tissue padding the calcaneus and medial metatarsal heads (low-order models). The high-order whole-foot model provides real-time analytical evaluations of the time-dependent plantar fascia tensile forces during the stance phase. These force evaluations are transferred, together with foot-shoe local reaction forces, also measured in real time (under the calcaneus, medial metatarsals and hallux), to the low-order FE models of the plantar pad, where they serve as boundary conditions for analyses of local deformations and stresses in the plantar pad. After careful verification of our custom-made FE solver and of our foot model system with respect to previous literature and against experimental results from a synthetic foot phantom, we conducted human studies in which plantar tissue loading was evaluated in real time during treadmill gait in healthy individuals (N = 4). We concluded that internal deformations and stresses in the plantar pad during gait cannot be predicted from merely measuring the foot-shoe force reactions. Internal loading of the plantar pad is constituted by a complex interaction between the anatomical structure and mechanical behavior of the foot skeleton and soft tissues, the body characteristics, the gait pattern and footwear. Real-time FE monitoring of internal deformations and stresses in the plantar pad is therefore required to identify elevated deformation/stress exposures toward utilizing it in gait laboratories to protect feet that are susceptible to injury.
目前还没有技术能够在评估步态模式时提供有关个体足底软组织内部变形和应力的实时信息。由于足底垫的内部变形和应力是诸如糖尿病足溃疡等足部损伤的关键因素，这严重限制了对患者的评估。为了实现这种针对个体的实时分析，我们开发了一种分层建模系统，该系统将足部的二维总体结构模型（高阶模型）与填充跟骨和内侧跖骨头的足底组织的局部有限元（FE）模型（低阶模型）集成在一起。高阶全足模型可在站立阶段实时分析随时间变化的足底筋膜拉力。这些力的评估结果连同同样实时测量的（在跟骨、内侧跖骨和拇趾下方）足-鞋局部反作用力一起，被传递到足底垫的低阶FE模型中，在那里它们作为分析足底垫局部变形和应力的边界条件。在根据先前文献并对照合成足模的实验结果对我们定制的FE求解器和足部模型系统进行仔细验证之后，我们对健康个体（N = 4）在跑步机上行走时的足底组织负荷进行了实时评估的人体研究。我们得出结论，仅通过测量足-鞋力反应无法预测步态期间足底垫的内部变形和应力。足底垫的内部负荷是由足部骨骼和软组织的解剖结构与力学行为、身体特征、步态模式和鞋类之间的复杂相互作用构成的。因此，需要对足底垫的内部变形和应力进行实时有限元监测，以识别增加的变形/应力暴露，以便在步态实验室中利用它来保护易受伤的足部。
