[论文解读] Contribution of the transverse arch to foot stiffness in humans

Ali Yawar, Lucia Korpas+3 more|arXiv (Cornell University)|Jun 14, 2017

Lower Extremity Biomechanics and Pathologies被引用 5

一句话总结

本研究表明，通过远端横韧带将矢状面弯曲与横平面拉伸机械耦合，跖横弓显著增强了足中段的刚度。通过胶带加固足底前部以增强跖横弓，使足中段刚度提高了53%，揭示了一种此前被忽视的机制，其在弹性能量储存和推进方面的作用与跖筋膜和风系机制相当。

ABSTRACT

Stiffness of the human foot is central to its mechanical function, such as elastic energy storage and propulsion. Its doubly-arched structure, manifested as longitudinal and transverse arches, is thought to underlie the stiff nature. However, previous studies have focused solely on the longitudinal arch, and little is known about whether and how the transverse arch impacts the foot's stiffness. The common observation that a flexible currency bill significantly stiffens upon curling it transversally underlies our hypothesis that the transverse arch dominates the foot's stiffness. Through human subject experiments, we show that transversally reinforcing the ball of the foot by means of sports tape can increase the midfoot bending (dorsiflexion) stiffness by 53% on average. Such a result is possible if and only if midfoot bending is mechanically coupled with splaying of the distal metatarsal heads, thus engaging the distal transverse ligament. Using a simplified foot model, we elucidate a mechanism for such coupling to arise because of the transverse arch; namely transverse curvature couples sagittal plane bending with stretching along the transverse direction. We therefore conclude that the previously ignored distal metatarsal transverse ligaments, by way of the transverse arch, likely underlie the midfoot's elastic response by an amount comparable to or surpassing the plantar fascia, the windlass mechanism and other longitudinal tissues. Our findings impact current practice in clinical, sports and evolutionary biomechanics that focus solely on the longitudinal arch and on two-dimensional sagittal plane mechanics.

研究动机与目标

• 研究跖横弓在人类足部刚度中的作用，该作用长期以来被纵弓所掩盖。
• 检验假设：足中段横弓的增强可因远端横韧带的激活而提高刚度。
• 阐明由于跖横弓曲率导致的矢状面弯曲与横平面变形之间的机械耦合机制。
• 挑战当前生物力学范式，该范式仅强调矢状面力学及跖筋膜等纵弓结构。

提出的方法

• 通过足中段背屈刚度测量，在人类受试者中开展实验，比较跖横弓胶带固定前后的情况，以模拟其增强效果。
• 在足底前部应用运动胶带，限制远端跖骨头的外展，从而增加横弓刚度。
• 使用简化的机械足部模型，展示横弓曲率如何将矢状面弯曲与横平面拉伸耦合。
• 通过几何原理分析机械耦合机制，将横平面曲率与矢状面阻力联系起来。
• 通过背屈角度与施加载荷的测量，量化不同胶带固定条件下足中段的刚度变化。
• 通过约束横平面变形时刚度的变化，推断远端横韧带的作用。

实验结果

研究问题

• RQ1 通过胶带增强跖横弓是否能显著提高人类足中段的刚度？
• RQ2 矢状面弯曲与横平面变形之间的机械耦合是否导致刚度增加？
• RQ3 与跖筋膜和风系机制相比，跖横弓在足部刚度中贡献了多少？
• RQ4 仅靠跖横弓的曲率是否足以通过机械耦合解释观察到的刚度增强？
• RQ5 远端横韧带在行走过程中对足部弹性响应的贡献如何？

主要发现

• 通过胶带对足中段进行横弓增强，平均使足中段背屈刚度提高了53%，证明了其直接的机械效应。
• 只有当足中段弯曲与远端跖骨头外展机械耦合时，刚度才得以提升，表明韧带参与。
• 跖横弓的曲率创造了矢状面弯曲与横平面拉伸之间的机械耦合，从而增强了刚度。
• 远端横韧带对足部刚度的贡献，可能与跖筋膜和风系机制相当，甚至更大。
• 研究结果表明，跖横弓在足中段刚度中起主导作用，挑战了长期以来生物力学模型仅关注纵弓的传统观念。
• 该机械机制可通过一个简化足部模型加以解释，该模型捕捉了平面间由曲率引起的耦合效应。