扁平足第二跖纵弓疲劳损伤的生物力学机制

目的 研究扁平足和正常足的第二跖骨与足底腱膜的过劳性损伤生物力学机理,对比分析步态周期中扁平足与正常足疲劳损伤的危险性,为制定临床防治措施提供定量化理论依据。方法 采用生物力学实验和计算医学手段,通过有限元方法和疲劳损伤理论分析,开展了步态周期中扁平足和正常足疲劳行为的计算机定量模拟,并通过足骨应力集中部位测定及足弓变形X线片测量来验证模型的可靠性。结果 建立了扁平足弹性足弓有限元模型,计算得到步态周期各个阶段扁平足第二跖骨和足底腱膜的动态应力峰值分别约为28．77MPa和12．53MPa,扁平足的第二跖骨动态应力比正常足增加了8％～21％,扁平足的足底腱膜动态应力比正常足增加了21％～51％。足底腱膜发炎或部分切除后扁平足和正常足的张拉应力都发生了转移,最大相对量转移发生于足底长韧带,最大绝对量转移发生于第二跖骨底,但扁平足的最后应力始终超过正常足0．26～5．32MPa。结论 无论扁平足或正常足,其应力集中部位均发生于第二跖骨和足底腱膜,但扁平足的疲劳应力峰值始终高于正常足。足底各类软组织中,足底腱膜承受的张拉应力最大,足底腱膜发炎或外科部分切除导致腱膜张拉应力转移,加剧了足底固有肌和长韧带的劳损,同时也增加了第二跖骨疲劳骨折的危险性。扁平足的足踝内旋,足弓塌陷,以及mu囊炎引发的第二跖骨槌状畸变,均可增加过劳性损伤的发病率。

Biomechanical mechanisms of overuse injuries of second plantar longitudinal arch in flatfoot

OBJECTIVE: To research biomechanical mechanism of overuse injuries of second metatarsal and plantar aponeurosis of flat foot and normal foot, to contrast injury risk of flat foot with that of normal foot in gait cycle, and to offer quantitative academic base for clinical therapeutic and preventive measures. METHODS: Biomechanical MTS test, computational medicine means, finite element method and fatigue injury theory were adopted, fatigue behavior of flat foot and normal foot in gait cycle was simulated quantificationally by computer, their models successfully validated by test of stress concentration of foot bones and X-ray measurement of arch deformation. RESULTS: The finite element model of elastic arch of flat foot was established, peak values of fatigue stresses of second metatarsal and plantar aponeurosis in flat foot were individually 28.77 MPa and 12.53 MPa, these stresses of flat foot increased individually 8% approximately 21% and 21% approximately 51% than those of normal foot. Transfer of tension stresses of both flat foot and normal foot took place when plantar aponeurosis got infected or released partially, relative maximum of stress transfer occurred in plantar ligament, absolute maximum of stress transfer occurred in base of second metatarsal, the final stress of flat foot always overrun 0.26 approximately 5.32 MPa than normal foot. CONCLUSION: Von Mises stresses of both flat foot and normal foot are concentrated on second metatarsal and plantar aponeurosis, but peak values of fatigue stresses of flat foot are higher than normal foot. Tension stress of plantar aponeurosis is maximum in all plantar soft tissues, plantar fasciitis or surgical partial release of plantar fascia leads to transfer of tension stresses, and can aggravate overuse injury of plantar muscles and plantar ligament, also can add risk of fatigue fracture of second metatarsal. Internal rotation of flat foot, arch collapse, and hammer toe of second ray caused by bunions all can increase incidence rate of overuse injury in flat foot.