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摘要
人類於步行時，由於力量傳遞機制導致推進期間力量集中於第一與第二蹠骨頭(first and second metatarsal head)下方區域，所產生之不適與疼痛感稱為蹠骨痛(metatarsalgia)，而蹠骨墊(metatarsal pad)為臨床上常用於緩解該症狀之輔具。過去文獻已藉由足底壓力量測系統證實蹠骨墊具有減壓效益，然而此一實驗過程繁複且往往無法排除足部與蹠骨墊之間的相對位移且無法確切定義擺位。因此，如何擺放以及使用何種幾何外型之蹠骨墊具有較佳減壓效益仍未有定論。本研究藉由動態有限元素分析(dynamic finite element analysis)中對位準確及參數調整快速等優勢排除過去文獻中之實驗限制，探討不同蹠骨墊設計與擺放位置對於足底壓力分佈之影響。
研究過程中沿用本研究室過往已建構完整足部模型，配合以樑元素(beam element)取代實體足底筋膜(plantar fascia)以及鞋具、鞋面、鞋內墊(insole)與蹠骨墊之有限元素模型建構，並以步態實驗獲得之運動學與力動學結果作為有限元素分析邊界條件與模型驗證。完成模型驗證後，探討蹠骨墊五種擺放位置、兩種高度與三種面積尺寸變化對於蹠骨下方以及第二蹠骨頭下方區域之壓力變化影響。
有限元素分析結果顯示，當蹠骨墊置於第二蹠骨頭近心端(proximal)10mm時，相較於其他擺放位置具有較佳之減壓效果。當蹠骨墊置於適當擺放位置，高度由5mm增加至10mm後，能有效的增加蹠骨墊減壓效果，卻相對產生高壓力峰值集中之現象。而蹠骨墊面積尺寸由原尺寸增加10%後，能達到分散高壓力峰值集中之功效。因此，當蹠骨墊置於合宜的位置下，適當的增加蹠骨墊高度與面積尺寸，能增加蹠骨墊之減壓效果並避免高壓力峰值集中現象發生。本研究有限元素分析結果僅針對單一受測試者進行探討，受測試者之足部尺寸與型態則尚未考量。未來可藉由招募具有不同足部大小及型態之受測試者進行探討，以提供更為完整之參考建議。
Abstract
When people walk on the ground, their strengths are transmitted to the area below their first and second metatarsal heads through strength transmission mechanism. The pains and discomforts caused by the strength transmission process are collectively known as metatarsalgia. From clinical standpoint, metatarsal pad is a valuable assistive device that alleviates the symptom effectively. A number of literatures conclude that metatarsal pad has a satisfactory decompression performance based on the results obtained from plantar pressure measurement system. Nevertheless, the experiment itself is very complicated, unable to eliminate the relative displacement between foot and metatarsal pad, and unable to define the positioning precisely. As to the ideal positioning and the perfect geometrical profile of metatarsal pad needed for the best decompression performance, no definitive conclusion has been made so far. Dynamic finite element analysis is known for its unique attributes, such as precise alignment and swift adjustment of parameters. Therefore, this study attempted to identify the influence on the distribution of plantar pressure imposed by the design and positioning of metatarsal pad using dynamic finite element analysis in order not to be confined by the restrictions outlined in various literatures.
This study adopted the foot model constructed by the laboratory earlier; substituted beam element for the finite elements of plantar fascia, footwear, instep, insole, and metatarsal pad; acquired kinetic results and force pharmacokinetic results through gait experiments; and used these results as finite elements for the analysis of boundary conditions and model validation. After model validation was completed, this study switched between metatarsal pad’s five positions, two heights, and three dimensions, and thus discussed the changes of pressure in the area below metatarsal head and in the area below the second metatarsal head.
According to the results acquired from finite element analysis, when a metatarsal pad was placed in the proximal area within 10 mm to the second metatarsal head, the pad had better decompression performance than other metatarsal pads placed in any other position; when metatarsal pad was placed in a proper position and was lifted from 5mm to 10mm, the pad’s decompression performance improved effectively and meanwhile high pressure peak was concentrated; when metatarsal pad’s dimension increased by 10%, high pressure peak dispersed. Apparently, when metatarsal pad is placed in a proper position and meanwhile its height and dimension increase proportionately, its decompression performance improves and its high pressure peak disperses. This study acquired finite element analysis results from an experimental subject without consideration for the experimental subject’s foot dimension and pattern. When experimental subjects with different foot sizes and types are studied in the future, a perfect solution will be presented for reference.
