Cheng Hsin-Yi Kathy, Lin Chun-Li, Wang Hsien-Wen, Chou Shih-Wei
Graduate Institute of Mechanical Engineering, Chang Gung University, Kwei-Shan, Tao-Yuan 333, Taiwan.
J Biomech. 2008;41(9):1937-44. doi: 10.1016/j.jbiomech.2008.03.028. Epub 2008 May 27.
Stretching plays an important role in the treatment of plantar fasciitis. Information on the internal stresses/strains of the plantar fascia under stretch is useful in enhancing knowledge on the stretch mechanisms. Although direct measurement can monitor plantar fascia changes, it is invasive and gathers only localized information. The purpose of this paper was to construct a three-dimensional finite element model of the foot to calculate the stretch effects on plantar fascia and monitor its stress/strain distributions and concentrations. A three-dimensional foot model was developed and contained 26 bones with joint cartilages, 67 ligaments and a fan-like solid plantar fascia modeling. All tissues were idealized as linear elastic, homogeneous and isotropic whilst the plantar fascia was assigned as hyperelastic to represent its nonlinearity. The plantar fascia was monitored for its biomechanical responses under various stretch combinations: three toe dorsiflexion angles (windlass effect: 15 degrees , 30 degrees and 45 degrees ) and five Achilles tendon forces (100, 200, 300, 400 and 500N). Our results indicated that the plantar fascia strain increased as the dorsiflexion angles increased, and this phenomenon was enhanced by increasing Achilles tendon force. A stress concentration was found near the medial calcaneal tubercle, and the fascia stress was higher underneath the first foot ray and gradually decreased as it moved toward the fifth ray. The current model recreated the position of the foot when stretch is placed on the plantar fascia. The results provided a general insight into the mechanical and biomechanical aspects of the influences of windlass mechanism and Achilles tendon force on plantar fascia stress and strain distribution. These findings might have practical implications onto plantar fascia stretch approaches, and provide guidelines to its surgical release.
伸展运动在足底筋膜炎的治疗中起着重要作用。了解足底筋膜在伸展状态下的内部应力/应变情况，有助于增进对伸展机制的认识。尽管直接测量可以监测足底筋膜的变化，但它具有侵入性，且只能收集局部信息。本文的目的是构建一个足部三维有限元模型，以计算对足底筋膜的伸展效果，并监测其应力/应变分布及集中情况。开发了一个足部三维模型，其中包含26块带有关节软骨的骨头、67条韧带以及一个扇形实体足底筋膜模型。所有组织均被理想化为线性弹性、均匀且各向同性的，而足底筋膜被设定为超弹性以体现其非线性特性。在各种伸展组合下监测足底筋膜的生物力学反应：三个足趾背屈角度（跖腱膜绞盘效应：15度、30度和45度）以及五个跟腱力（100、200、300、400和500牛）。我们的结果表明，随着背屈角度的增加，足底筋膜应变增大，并且这种现象会因跟腱力的增加而增强。在内侧跟骨结节附近发现了应力集中，并且在第一跖骨下方的筋膜应力较高，并随着向第五跖骨移动而逐渐降低。当前模型再现了对足底筋膜施加伸展时足部的位置。这些结果为跖腱膜绞盘机制和跟腱力对足底筋膜应力和应变分布影响的力学和生物力学方面提供了总体认识。这些发现可能对足底筋膜伸展方法具有实际意义，并为其手术松解提供指导。
