Establishment and application of a finite element model of the foot structure

doi:10.3969/j.issn.2095-4344.2016.29.017

Abstract

Abstract:

BACKGROUND: The finite element analysis used to study the biomechanical properties of foot structure contributes to overcome the disadvantages of traditional mechanical analysis of specimens.
OBJECTIVE: To summarize some representative finite element models of the foot and review the establishment methods of finite element models of the foot with biomechanical properties.
METHODS: A computer-based online search was conducted in CNKI, Wanfang and PubMed databases by using the key words of “finite element model, biomechanic, foot structure” from 1999 to 2015. The language was limited to both Chinese and English. Establishment methods of finite element models of the foot structure containing obtaining of model establishment data, establishment of solid model, setting methods of properties of model materials. The application of finite element analysis of the foot structure in sports biomechanics and medical orthotics was summarized to point the characteristics and disadvantages of finite element analysis application in biomechanics.
RESULTS AND CONCLUSION: An increasing number of studies on foot biomechanics provide the platform for finite element analysis of the foot applied in biomechanical analysis. Many key technologies, including self-adaption image segmentation method, hexahedron grid product method and establishment of finite element models with various materials have to be utilized to converse the medical images into digital models of finite element analysis during establishment of finite element models. Results of model establishment may be affected by limitation conditions, accuracy of image collection, calculation results of finite element analysis. The reliability of finite element models can be increased by modify technologies and verification methods.

中国组织工程研究杂志出版内容重点：组织构建；骨细胞；软骨细胞；细胞培养；成纤维细胞；血管内皮细胞；骨质疏松；组织工程

Key words: Finite Element Analysis, Biomechanics, Foot

CLC Number:

R318

Song Ya-wei, You Chuan-bao, Yu Wen-bing. Establishment and application of a finite element model of the foot structure[J]. Chinese Journal of Tissue Engineering Research, 2016, 20(29): 4376-4382.

Figures/Tables 1

2.1 足部有限元模型几何参数数据的采集有限元分析法在解决足部生物力学问题中的研究取得巨大进展，医学图像以无创的方式结合图像处理技术及可视化技术可使个性化模型乃至生物力学仿真的有限元模型建立成为可能。来自计算机断层扫描术(CT)和磁共振成像的医学图像包含了丰富的人体解剖结构的几何和材质信息，应用生物医学图像处理技术、可视化和网格生成技术，能过建立基于医学图像的个性化模型。 2.1.1 CT图像近年来国外相继建立了基于X射线片、CT及磁共振成像技术的足部有限元模型。CT是在不破坏物体结构的前提下，探测物体周边的某种物理量的数据，借助计算机的运算能力，经过一定的数学模型计算处理后，重构组织的三维图像的技术。国内外许多学者提出了一种基于人体CT断层图像提取组织边界，并根据提取到的真实边界进一步快速且精确的建立足部三维有限元模型的方法。利用该方法最终可建立含有真实结构信息的人体有限元模型，并应用有限元分析其力学特性来评价建模方法具有独特的优势。以往CT图像的测试结果证实，该方法简单、快捷、适应性强，为基于医学图像的有限元分析奠定了良好基础[15-16]。牛文鑫等[17]为验证通过对序列螺旋CT图片处理建立的足部三维实体模型的有效性，对7具新鲜离体标本进行实验，在电子万能试验机加载条件下，用数字散斑相关法测量位移，实验结果充分论证了模型的有效性和临床应用安全性。以上结果说明，通过CT采集序列断层图像，并在数字化和阈值分割的基础上将断层图像中的微结构信息映射到重构的有限元网格模型中，使得人体组织中的任何细节结构信息都可以在重构模型中得到重现。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，通过CT数据来三维重建人足包括骨骼、主要韧带、皮肤及软组织在内的主要结构的有限元模型，对跗跖关节进行准稳态有限元受力分析。进行了在正常及模拟碾压伤情况下跗跖关节有限元应力分析，得到了跗跖关节应力云图，间接证实了试验有限元模型的可靠性。以此方法来揭示跗跖关节解剖结构特点，探讨人足受力与跗跖关节损伤之间的关系，为解释跗跖关节损伤机制提供有限元模拟生物力学方面的理论依据[18-19]。卢昌怀等[20]基于志愿者足的三维CT扫描数据，建立一个具有高度几何相似性的足踝部三维有限元模型，经验证是一个正确可靠的模型，可以帮助临床医生和其他研究人员更好的理解正常步态下距骨的许多生物力学特性。 2.1.2 磁共振成像磁共振是核磁共振成像由于应用到电磁技术成像，和以往检查手段如X射线以及CT比较有很大的区别，其可以多序列成像、多种图像类型，为明确病变性质提供更丰富的影像信息。磁共振成像医学图像包含了丰富的人体解剖结构的几何和材质信息，应用生物医学图像处理技术、可视化和网格生成技术，使得基于医学图像的个性化建模成为可能。研究证明根据磁共振成像图像数据建立的三维模型，比CT扫描数据建立的模型更接近于真实解剖结构[21-22]。杨滨等[23]基于磁共振成像数据精确构建三维实体模型，认为该模型可用于三维有限元应力分析，为深入对其进行生物力学研究提供技术支撑。基于磁共振图像建立的踝关节三维有限元模型，经验证是一个仿真度高、可靠性好的模型，可以帮助临床工作者和其他相关人员更好的理解踝关节的各种生物力学特性[24-25]。近年来通过对磁共振成像的研究进一步了解到足部的运动和病变，并提供了足部软骨的形态信息。磁共振成像已广泛用于软骨厚度和体积的测试。有研究证实基于磁共振成像的有限元分析法可高度模拟人体结构与材料特性，对实验条件高度仿真，建立直观形象的三维图像，准确反映局部与整体信息，显示出极大的优越性，为足部疾病病因、病理及治疗的临床研究提供了有力支持[26-27]。 2.1.3 三维激光扫描测量在X射线摄片、CT、磁共振成像等静态二维图像上难以反映各结构的空间位置关系及运动轨迹。三维激光扫描技术是一种建立在测量学科、仪器光电子学科，图形图像处理等多种学科基础上的综合性技术，以其方便、快捷的以高精度、密度方式并且是无接触形式获得研究对象的三维点云数据，在国内外得到了广泛的应用。三维激光扫描测量与CT扫描重建技术相比具有一定优势，是一种具有良好发展前景的临床数字模型解决方案[28-29]。李秀忠等[30]采用较为先进的三维激光扫描技术，利用计算机重建的三维影像准确显示骨性结构立体形态的同时，详细了解到解剖结构的空间关系，采集到在标本加载或运动状态下的信息，提供了一种准确、便捷的研究手段。董海东等[31]利用三维激光扫描技术成功地建立了三维有限元建模，利用有限元软件进行网格划分生成有限元模型的方法是可行的，并保证了很好的几何相似性。同样有研究也发现应用三维激光扫描技术所建立的有限元模型仿真效果好、精确度高，利用三维激光扫描技术可以快捷、准确的建立三维几何模型和有限元模型，以满足临床工作的需要[32-33]。由于三维激光扫描仪操作简单，具有自动化程度高、可无接触测量等优势，已经成为建立有限元模型的重要手段。 2.2 足部有限元模型生物力学的验证对于逼真的足部各结构有限元模型构建中有限元模型材料属性设定的方法，往往采用同一性处理，使得通常的力学实验手段很难精确地对其进行研究。基于CT及磁共振成像的有限元分析法可高度模拟人体结构与材料特性，对实验条件高度仿真，建立直观形象的三维图像，准确反映局部与整体信息，显示出极大的优越性。建立高质量的有限元模型是进行力学分析研究的前提条件，对足部的材料的特性和建模数据的获取的研究是基础。"

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