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.     

面向逆向动力学仿真驱动和验证的半蹲式跳伞着陆实验研究

目的半蹲式跳伞着陆模拟实验的设计和相关数据测量,为逆向动力学软件AnyBodyModelingSystem模型的建立、驱动和验证提供数据。方法根据逆向动力学分析数据驱动和验证的需要,受试者从0.32m高的平台跳落,模拟半蹲式跳伞着陆。对受试者下肢关节运动学参数、地面反力以及下肢4块主要肌肉的肌电图进行测量。结果受试者在与地面接触前后1s内,髋、膝、踝关节角度随时间的变化、右脚地面反力以及压力中心轨迹用来驱动模型;肌电活动性测量数据用来验证模型。结论实验设计可以满足肌骨模型分析的要求,并可用于对半蹲式跳伞着陆的进一步研究。     

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.     

Development and Validation of a Computational Model to Study the Effect of Foot Constraint on Ankle Injury due to External Rotation

Recent studies, using two different manners of foot constraint, potted and taped, document altered failure characteristics in the human cadaver ankle under controlled external rotation of the foot. The posterior talofibular ligament (PTaFL) was commonly injured when the foot was constrained in potting material, while the frequency of deltoid ligament injury was higher for the taped foot. In this study an existing multibody computational modeling approach was validated to include the influence of foot constraint, determine the kinematics of the joint under external foot rotation, and consequently obtain strains in various ligaments. It was hypothesized that the location of ankle injury due to excessive levels of external foot rotation is a function of foot constraint. The results from this model simulation supported this hypothesis and helped to explain the mechanisms of injury in the cadaver experiments. An excessive external foot rotation might generate a PTaFL injury for a rigid foot constraint, and an anterior deltoid ligament injury for a pliant foot constraint. The computational models may be further developed and modified to simulate the human response for different shoe designs, as well as on various athletic shoe–surface interfaces, so as to provide a computational basis for optimizing athletic performance with minimal injury risk.     

Non-linear flexion relationships of the knee with the hip and ankle, and their relative postures during landing

The knee joint, together with the hip and ankle, contributes to overall shock absorption through their respective flexion motions during landing. This study sought to investigate the presence of a lower extremity coordination pattern by determining mathematical relationships that associate knee flexion angles with hip flexion and ankle dorsiflexion angles during landing phase, and to determine relative postures of the hip and ankle, with reference to the knee, and examine how these relative postures change during key events of the landing phase. Eight healthy male subjects were recruited to perform double-leg landing from 0.6-m height. Motion capture system and force-plates were used to obtain kinematics and ground reaction forces (GRF) respectively. Non-linear regression analysis was employed to determine appropriate mathematical relationships of the hip flexion and ankle dorsiflexion angles with knee flexion angles during the landing phase. Relative lower extremity postures were compared between events of initial contact, peak GRF and maximum knee flexion, using ANOVA on ranks. Our results demonstrated a lower extremity coordination pattern, whereby the knee flexion angles had strong exponential (R² = 0.92–0.99, p < 0.001) and natural logarithmic (R² = 0.85–0.97, p < 0.001) relationships with hip flexion and ankle dorsiflexion angles respectively during the landing phase. Furthermore, we found that the subjects adopted distinctly different relative lower extremity postures (p < 0.05) during peak GRF as compared to initial contact. These relative postures were further maintained till the end of the landing phase. The occurrence of these relative postures may be a reflexive mechanism for the subjects to efficiently absorb the impact imposed by the peak GRF.     

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。     

Biomechanical analysis of fatigue-related foot injury mechanisms in athletes and recruits during intensive marching

An integrative analysis, comprising radiographic imaging of the foot, plantar pressure measurements, surface electromyography (EMG) and finite element (FE) modelling of the three-dimensional (3D) foot structure, was used to determine the effects of muscular fatigue induced by intensive athletic or military marching on the structural stability of the foot and on its internal stress state during the stance phase. The medial/lateral (M/L) tendency towards instability of the foot structure during marching in fatigue conditions was experimentally characterised by measuring the M/L deviations of the foot-ground centre of pressure (COP) and correlating these data with fatigue of specific lower-limb muscles, as demonstrated by the EMG spectra. The results demonstrated accelerated fatigue of the peroneus longus muscle in marching conditions (treadmill march of 2km completed by four subjects at an approximately constant velocity of 8 kmh⁻¹). Severe fatigue of the peroneus longus is apparently the dominant cause of lack of foot stability, which was manifested by abnormal lateral deviations of the COP during the stance phase. Under these conditions, ankle sprain injuries are likely to occur. The EMG analysis intensive marching (averaged decreases of 36% and 40% in the median frequency of their EMG signal spectra, respectively). Incorporation of this information into the 3D FE model of the foot resulted in a substantial rise in the levels of calcaneal and metatarsal stress concentrations, by 50% and 36%, respectively. This may point to the mechanism by which stress fractures develop and provide the biomechanical tools for future clinical investigations.     

A Finite Element Model of the Lower Limb for Simulating Automotive Impacts

A finite element (FE) model of a vehicle occupant’s lower limb was developed in this study to improve understanding of injury mechanisms during traffic crashes. The reconstructed geometry of a male volunteer close to the anthropometry of a 50th percentile male was meshed using mostly hexahedral and quadrilateral elements to enhance the computational efficiency of the model. The material and structural properties were selected based on a synthesis of current knowledge of the constitutive models for each tissue. The models of the femur, tibia, and leg were validated against Post-Mortem Human Surrogate (PMHS) data in various loading conditions which generates the bone fractures observed in traffic accidents. The model was then used to investigate the tolerances of femur and tibia under axial compression and bending. It was shown that the bending moment induced by the axial force reduced the bone tolerance significantly more under posterior-anterior (PA) loading than under anterior-posterior (AP) loading. It is believed that the current lower limb models could be used in defining advanced injury criteria of the lower limb and in various applications as an alternative to physical testing, which may require complex setups and high cost.     

太极拳转体动作中下肢关节活动顺序性和肌肉力表现及肌肉激活特征

目的 分析太极拳转体与弓步动作中下肢关节活动顺序性、肌肉力表现和肌肉激活程度的差异,揭示太极拳转体动作的特征。 方法 募集 20 名练习时长超过 3 年的健康太极拳练习者,采用三维运动捕捉系统、测力台和表面肌电同步采集转体与弓步两种动作运动学、动力学和肌肉激活信息,并通过 OpenSim 仿真软件获取下肢肌力。结果 与弓步相比,转体动作髋、踝关节外旋幅度显著增大;膝关节外展和外旋力矩显著增大,股二头肌、半腱肌和内外侧腓肠肌峰值肌力显著增强,股二头肌、内外侧腓肠肌峰值肌力时刻显著提前,而股内外侧肌和胫骨前肌峰值肌力显著减小,胫骨前肌肌力最早达到峰值;股二头肌、股内外侧肌和内侧腓肠肌的平均激活水平和激活时间显著增加。 结论 太极拳转体动作由踝、髋关节依次转动组成,肌肉力表现的独特性在于重心两次转移致使支撑腿内外侧肌力曲线呈双峰型,因为全足着地延迟方式引发了腓肠肌与股四头肌激活顺序和肌肉平均激活水平改变。研究结果提示全足着地延迟方式具有调节肌肉激活顺序的作用,合理利用有助于提升临床康复效果。     

Effects of static high compression on human foot-ankle: biomechanical response and injuries

To reduce road-traffic fatalities, significant improvements have been seen in the protection of vital body parts. Attention is now focused on serious injuries, which cause disability or impairment as lower limb injuries. The numerical models developed to have a better understanding of injury parameters are evaluated from human responses to load. For this objective, mechanical characterisation tests have been performed on nine human foot/ankle specimens. The responses of three foot contact points during various static loads of the tibia were studied. After each test, an autopsy was performed and the associated injuries were noticed. These tests allowed quantification of the tibia compressive force in relation to foot and ankle deformations up to injury level.     

使用有限元法模拟枕寰枢复合体的中性区

目的为枕颈部中性区（NZ）的研究建立有效的数学模型。方法本研究基于可视人数据库建立了枕寰枢复合体的非线性有限元模型,通过细致的轮廓提取和准确的材料特性定义,以提升上颈椎有限元模型的精确性。模型模拟了在静态生理载荷作用下复合体轴向旋转、前屈、后伸和侧弯运动。结果模型预测的运动范围（ROM）和NZ与实验数据相吻合。模型的力矩-转动关系呈明显的非线性关系,最大旋转发生在水平面,其次是正中矢状面和冠状面,且轴向旋转与侧弯相互耦合。模型总体表现出较大的ROM和较高比例的NZ。结论现有文献中尚未见到能同时成功验证ROM和NZ的上颈椎有限元模型。此模型可为枕颈部病变与创伤中出现的异常NZ的研究提供有力的辅助。     

跳伞着陆过程中膝关节损伤的有限元研究

目的利用膝关节有限元模型和模拟跳伞着陆实验数据,对半蹲式跳伞着陆过程进行数值模拟,并分析膝关节损伤的机理。方法对16名健康志愿者进行半蹲式模拟跳伞实验,跳落高度分别为0.32m,0.52m和0.72m。基于核磁共振成像建立人体膝关节的三维有限元模型,采用实验测得的膝关节运动学和地面反力数据对跳伞着陆过程进行数值模拟。结果关节内组织的应力水平随着跳落高度的增加而增加,外侧半月板和关节软骨承受了较大的载荷,前交叉韧带和内侧副韧带在屈膝角度达到最大时产生明显的应力集中。结论跳伞着陆的高速冲击是造成关节损伤的直接原因,外侧关节软骨和半月板更易受到损伤,前交叉韧带和内侧副韧带较易在屈膝幅度最大时发生撕裂。     

Asymmetry of the active nonweightbearing foot and ankle range of motion for dorsiflexion-plantar flexion and its coupled movements in adults

Asymmetries in ankle range of motion (ROM) have been reported, but often the uninvolved limb is used as a reference in clinical practice. The study wanted to quantify the intraindividual asymmetries in dorsi-plantar flexion foot and ankle ROM and its coupled foot movements. Active triplanar nonweightbearing ROM of the foot and ankle was recorded in young healthy adults (30 male volunteers, mean age 22.8 years; 35 female volunteers, mean age 23.8 years) using an optoelectronic set-up. The sagittal plane movement (mean ROM female subjects right side 71.3 degrees, left side 71.4 degrees, P > 0.05; mean ROM male subjects right side 69 degrees , left side 68.9 degrees, P > 0.05; sex difference, P < 0.001) was coupled with frontal (mean ROM female subjects right side 16.6 degrees, left side 14.8 degrees, P > 0.05; male subjects right side 17 degrees, left side 15.3 degrees; P > 0.05; no sex difference) and horizontal (mean ROM female subjects right side 19.6 degrees, left side 18.8 degrees, P < 0.001; male subjects right side 17.6 degrees, left side 16.2 degrees, P < 0.001; sex < 0.001) plane motions. Individual fluctuating asymmetries up to 15 degrees (principal movement), and up to 29 degrees (associated movements) were measured. Overall, 20% of female and 34% of male subjects had principal plane asymmetries >5 degrees, and 50% of the subjects had asymmetries >5 degrees in the associated movements. In young adults, individual asymmetries in ankle joint complex dorsi-plantar flexion should be taken into account when using the uninvolved, contralateral limb as a reference for clinical examination.     

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。     

足部三维有限元建模方法及其生物力学应用

目的探讨建立足部三维有限元模型的方法,应用模型模拟分析研究鞋垫设计参数,不同软组织刚度和受力情况下对足部的生物力学影响。方法建立基于解剖结构,包括软组织,韧带和腱膜,考虑材料的非线性和关节接触的足部三维有限元模型。有限元模型的可靠性利用模拟足踝关节在不同病理、手术和鞋垫矫治情况下的生物力学反应来验证。结果有限元分析结果表明,定制型鞋垫的形状比鞋垫材料的刚度对减少足底最大压力有更重要影响。软组织刚度的增加引起足底接触面积的减小,从而会导致足底跖骨区最大压力增加。部分和完全松解足底腱膜都会降低足弓高度,并增加足底韧带的张力和增加中足和跖骨的应力。体重增加和跟腱拉力增加都将成倍足底筋膜的拉力。结论所建足部有限元模型能预测足底压力分布和足内部骨骼软组织应力、应变情况,可以成为设计鞋垫和研究足部各种临床状况提供有力的分析工具。     

Foot force direction in an isometric pushing task: prediction by kinematic and musculoskeletal models

The abilities of a kinematic model and a muscle model of the human lower limb to predict the stereotyped direction of the muscular component of foot force produced by seated subjects in a static task were tested and compared. Human subjects (n=11) performed a quasi-static, lower-limb pushing task against an instrumented bicycle pedal, free to rotate about its own axis, but with the crank fixed. Each pushing trial consisted of applying a force from the resting level to a force magnitude target with the right foot. Ten force target magnitudes were used (200, 250, …, 650 N) along with 12 pedal positions. For each pushing effort, the muscular contribution to the measured foot force was determined from push onset to peak attained force. This segment was well characterized by a straight line across subjects, pedal positions, and force target magnitudes. The linear nature of the muscular component allowed a characteristic direction to be determined for each trial. A three-joint (hip, knee, and ankle) and a two-joint (hip and knee) net joint torque optimization was applied to a sagittal-plane kinematic model to predict the characteristic force direction. A musculoskeletal model was also used to create a feasible force space (FFS) for the lower limb. This FFS represents the range of possible forces the lower limb could theoretically produce. From this FFS, the direction of the maximum feasible foot force was determined and compared with the characteristic direction of subject performance. The muscle model proved to be the most effective in predicting subject force direction, followed by the three-joint and two-joint net joint torques optimizations. Similarities between the predictions of the kinematic and muscle model were also found. Electronic Publication     

前韧带加强修复结合螺钉固定用于下胫腓不稳的生物力学特性分析

目的 建立踝关节骨折固定后遗留下胫腓前韧带损伤,用锚钉加强修复结合螺钉固定的有限元模型,比较其受力及变形情况.方法 选取1例正常男性青年志愿者踝关节CT图像,建立踝关节骨折固定后遗留下胫腓前联合损伤有限元模型,对损伤模型置入锚钉固定为实验组,使用螺钉固定为对照组.通过有限元分析计算,观察两组模型在各种载荷工况下的最大应...     

下肢运动信息采集与运动仿真

目的 建立人体下肢3D模型与生物力学模型,进行运动学和动力学分析,搭建下肢控制平台为主动式下肢假肢和人体下肢助行器的控制研究提供理论依据。方法 利用VICON人体三维运动捕捉系统采集平地行走人体下肢髋、膝、踝运动信息。利用Solidworks建立人体下肢3D模型,进行下肢运动学分析。基于Matlab中Simulink的机械仿真模块（SimMechanics）建立人体下肢模型,进行动力学分析,产生运动信号。基于Quanser半实物仿真平台搭建控制模型,接收SimMechanics产生的运动控制信号,实现对双下肢运动平台的控制。结果 利用运动学分析得到各个关节的速度和加速度信号,利用动力学仿真得到各个关节的力矩信号,对建立的人体双下肢模型进行模拟仿真,通过仿真验证了模型的合理性,利用输出的信号对双下肢运动平台进行控制实现了平地行走功能。结论 建立的平台可以进行人体下肢运动学、动力学和控制方法的研究,为主动式假肢和人体下肢助行器的控制提供借鉴作用。     

A Population of Patient-Specific Adult Acquired Flatfoot Deformity Models Before and After Surgery

Following IRB approval, a cohort of 3-D rigid-body computational models was created from submillimeter MRIs of clinically diagnosed Adult Acquired Flatfoot Deformity patients and employed to investigate postoperative foot/ankle function and surgical effect during single-leg stance. Models were constrained through physiologic joint contact, passive soft-tissue tension, active muscle force, full body weight, and without idealized joints. Models were validated against patient-matched controls using clinically utilized radiographic angle and distance measures and plantar force distributions in the medial forefoot, lateral forefoot, and hindfoot. Each model further predicted changes in strain for the spring ligament, deltoid ligament, and plantar fascia, as well as joint contact loads for three midfoot joints, the talonavicular, navicular-1st cuneiform, and calcaneocuboid. Radiographic agreement ranged across measures, with average absolute deviations of <5° and <4 mm indicating generally good agreement. Postoperative plantar force loading in patients and models was reduced for the medial forefoot and hindfoot concomitant with increases in the lateral forefoot. Model predicted reductions in medial soft-tissue strain and increases in lateral joint contact load were consistent with in vitro observations and elucidate the biomechanical mechanisms of repair. Thus, validated rigid-body models offer promise for the investigation of foot/ankle kinematics and biomechanical behaviors that are difficult to measure in vivo.     

膝关节假体股胫接触面积的影响因素

目的通过建立自动化流程对膝关节假体股胫接触面积的影响因素进行分析,总结设计参数对接触面积的影响规律,并找到最大接触应力和接触面积之间的关系。方法在Isight中建立参数化有限元模型,包括几何模型自动变参、自动化有限元前处理和有限元运算3个组件,实现自动化流程,提取接触面积进行统计学分析。结果有限元模型用Tekscan应力分布系统进行验证。当股骨、胫骨矢状面半径逐渐接近时,接触面积最大为295 mm~2。股骨矢状面半径对接触面积是正效应,而胫骨矢状面半径是负效应。最大接触应力和接触面积近似呈线性负相关。结论通过分析股胫矢状面半径对接触面积和接触应力的影响规律,为临床降低衬垫磨损提供设计依据。