A Finite Element Model of the Foot and Ankle for Automotive Impact Applications

A finite element (FE) model of the foot and leg was developed to improve understanding of injury mechanisms of the ankle and subtalar joints during vehicle collisions and to aid in the design of injury countermeasures. The FE model was developed based on the reconstructed geometry of a male volunteer close to the anthropometry of a 50th percentile male and a commercial anatomical database. While the forefoot bones were defined as rigid bodies connected by ligament models, the surrounding bones of the ankle and subtalar joints and the leg bones were modeled as deformable structures. The material and structural properties were selected based on a synthesis of current knowledge of the constitutive models for each tissue. The whole foot and leg model was validated in different loading conditions including forefoot impact, axial rotation, dorsiflexion, and combined loadings. Overall results obtained in the model validation indicated improved biofidelity relative to previous FE models. The developed model was used to investigate the injury tolerance of the ankle joint under brake pedal loading for internally and externally rotated feet. Ligament failures were predicted as the main source of injury in this loading condition. A 12% variation of failure moment was observed in the range of axial foot rotations (±15°). The most vulnerable position was the internally rotated (15°) posture among three different foot positions. Furthermore, the present foot and ankle model will be coupled together with other body region FE models into the state-of-art human FE model to be used in the field of automotive safety.     

有限元法在足踝生物力学研究中的应用进展

有限元法以其高效、精确、可重复利用等特点成为生物力学研究的有效工具。由于足踝部位复杂的解剖结构和运动特性,有限元法可以借助强大的仿真建模和数据计算能力解决真实实验难以解决的问题,具有独特的优势并得到了广泛应用。本文归纳整理了近5年来国内外应用有限元法研究足踝生物力学问题的文献资料,从足踝在不同运动状态下的生物力学分析、组织特性研究、临床治疗分析以及支具与鞋的研究4个方面进行综述,为足踝生物力学的研究提供理论参考,并对未来有限元法在足踝生物力学领域的应用发展提供新思路。     

A Finite Element Model of the Foot/Ankle to Evaluate Injury Risk in Various Postures

The foot/ankle complex is frequently injured in many types of debilitating events, such as car crashes. Numerical models used to assess injury risk are typically minimally validated and do not account for ankle posture variations that frequently occur during these events. The purpose of this study was to evaluate a finite element model of the foot and ankle accounting for these positional changes. A model was constructed from computed tomography scans of a male cadaveric lower leg and was evaluated by comparing simulated bone positions and strain responses to experimental results at five postures in which fractures are commonly reported. The bone positions showed agreement typically within 6° or less in all anatomical directions, and strain matching was consistent with the range of errors observed in similar studies (typically within 50% of the average strains). Fracture thresholds and locations in each posture were also estimated to be similar to those reported in the literature (ranging from 6.3 kN in the neutral posture to 3.9 kN in combined eversion and external rotation). The least vulnerable posture was neutral, and all other postures had lower fracture thresholds, indicating that examination of the fracture threshold of the lower limb in the neutral posture alone may be an underestimation. This work presents an important step forward in the modeling of lower limb injury risk in altered ankle postures. Potential clinical applications of the model include the development of postural guidelines to minimize injury, as well as the evaluation of new protective systems.     

基于有限元模型分析不同蹬冰角度足踝部应力分布差异

目的 模拟仿真不同蹬冰角度足踝部的应力,通过优化分析得到合理的蹬冰角度与足踝部应力的定量关系。 方法 建立冰球鞋-足踝耦合有限元模型,三维拍摄获取冰球运动员的运动学参数进行模型验证与约束,计算对比 分析不同角度蹬冰动作的足踝部应力,构建多目标优化函数模型。 结果 在相同蹬冰角度下,胫腓骨应力最大,距 下关节应力次之,第 1 跖趾关节应力较小,足底筋膜应力最小。 随着蹬冰角度的减小,足踝部应力单调递增,胫腓 骨和足底筋膜应力变化幅度大,距下关节和第 1 跖趾关节应力变化幅度较小。 结论 在冰球运动启动阶段蹬冰过 程中,蹬冰角度与足踝不同部位应力呈反比例关系。 最佳蹬冰角度取决于对滑冰速度的期待值,如果给定速度与 应力承受之间的偏好系数,可通过优化方法计算出最优蹬冰角度。     

外侧楔形鞋垫对足踝生物力学影响的有限元分析

目的 探究外侧楔形鞋垫对足踝内部组织(包括足骨、关节和韧带)的生物力学影响。 方法 建立并验证足踝-鞋垫-地面三维有限元模型,探究步态 3 个关键瞬间赤足模型和鞋垫干预模型的足底压力分布、关节接触压力、跖骨及主要韧带的应力。 结果 5°外侧楔形鞋垫模型足底峰值压力比赤足模型减小 65. 8% 。 鞋垫干预使楔舟关节处峰值接触压力减小;距下关节处峰值接触压力和第 4、5 跖骨处峰值应力增大。 结论 本研究量化评估了外侧楔形鞋垫对足踝各部分的生物力学影响,提出了可适当减小外侧楔形鞋垫第 4、5 跖骨处倾斜角度的设计建议。     

精细乳腺有限元模型温度场的仿真与临床验证

为了研究乳腺肿瘤对体表温度分布的影响,本研究基于乳腺解剖学结构和生理学特征,建立了适合乳腺温度场分析的精细乳腺三维有限元模型。与传统乳腺模型相比,该模型更接近乳房生理结构,因此能更加准确的仿真出正常和嵌合肿瘤的乳腺温度场分布。本研究分别对传统均匀结构乳腺模型、正常精细结构乳腺模型和嵌合肿瘤精细乳腺模型进行了温度场分析,并与临床医学病例中的乳腺肿瘤热像图对比,发现结果吻合得很好。研究结果为乳腺癌的热成像检测提供了重要的参考依据。     

显微骨移植在踝足部关节融合术中的应用

踝足部是人体承受应力最大的部位.在踝足部病损中,以各种原因所致骨性关节炎、骨关节畸形及失稳状态最为常见,其治疗的终极措施每以各有关相邻关节面融合为主,以求达到矫正畸形、稳定关节和消除疼痛的目的,其中尤以踝关节与距跟关节融合术最为常用.但是踝足部关节融合有较高的失败率,有报道称,踝关节融合术后包括感染在内的并发症达5%~25%,其中假关节形成高达10%~25%[1,2].如何提高踝足部关节融合的成功率,并对该部位传统关节融合术后并发假关节者施行显微骨移植,以求早日恢复患者行走与负重功能,是显微足外科热点课题.多年来,笔者设计和创用了数种带血管蒂骨、骨膜移位植骨术以期达到上述目的.     

韧带和跖腱膜在足部有限元分析中的力学作用

目前通过建立足部三维有限元系统模型进行足部生物力学仿真已经逐渐被应用,而在大多数足部三维有限元模型的静态分析中,韧带和跖腱膜等软组织是通过直接连接骨骼上相应的附着点形成的索单元来模拟,而关节软骨把相邻的骨骼直接固连在一起.这种用关节软骨固连的方式代替真实的骨骼间的滑动摩擦,增强了骨骼间的结构强度,可能会造成原本由韧带等起到维持骨骼间相互作用却完全由关节软骨代替,即在有限元模型中,可能韧带等组织对仿真不起力学作用.本文的研究目的是在双足站立、静态载荷,关节采用固连方式时,分析足部三维有限元模型中有无韧带和跖腱膜对足部各种组织应力分布以及组织结构形态变化等的影响.     

拇外翻足三维有限元模型构建及其第1、2跖列生物力学分析

目的 建立拇外翻足有限元模型,研究不同拉力下第1、2跖列的应力及位移变化情况。方法 将采集的拇外翻病人足部CT图像导入Mimics软件,重建足部三维骨骼模型;利用3-matic软件对重建模型进行网格划分与体网格生成;将优化处理过的模型导入ANSYS中进行有限元分析,通过改变拉力大小、方向验证拉力与第1、2跖列的应力、位移之间的关系。结果 对第1近节趾骨施加不同大小、方向的拉力,当力小于12 N时,随着拉力的增加,第1趾骨位移变化较为明显,拉力每增大2 N,位移约增加1 mm;当力大于12 N时,随着拉力的增加,第1趾骨应力不断增加,而位移只发生微小变化;而当力保持12 N不变,以15°间隔改变力的方向时,第1、2跖列的应力大小及其分布随方向的变化而改变,同时位移也会产生相应的变化,且当力的方向与第2趾骨方向越趋于垂直时,第1趾骨产生的位移越大。结论 有限元分析技术可以形象、准确地分析第1、2跖列在不同拉力下的应力及位移变化情况,为拇外翻矫形器的设计奠定基础。