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。     

牙槽突植骨修复对腭裂上颌骨三维有限元模型的力学影响分析

通过对两种腭裂上颌骨模型的加力分析，研究牙槽突植骨手术对腭裂上颌骨模型的生物力学影响。我们采用17岁男性患者头颅CT扫描图像数据建立腭裂上颌骨三维有限元模型，通过叠加植骨块模型形成牙槽突植骨修复后的腭裂上颌骨模型。在上颌骨前端以正常上唇压力数值水平向后加载压力，观察压应力沿上颌骨分布的特点和剪应力及拉应力出现的位置。结果显示，压应力主要沿牙槽突分布，并形成数个应力集中区。植骨后，应力分布趋向均匀化。植骨可以降低由于上颌骨变形而产生的剪应力和牙槽突的向内移位。我们认为，唇裂修复手术后产生的压力可能是使牙槽突产生变形移位的主要原因，压应力沿着牙槽突骨弓传导可能使牙列畸形加重。牙槽突植骨修复可以使应力分布趋向均匀，但是不改变应力的分布特征。     

脊椎个性化模型的有限元分析：方法和精度的回顾

近十年来，通过医学图像的处理，建立脊椎个性化有限元模型的方法，随着计算方法的不断提高，得到了很大的发展。本文回顾了各种建模方法并对所生成模型的可靠精度做了评估。模型质量将受到网格密度和生成方法、材料属性分配和应用边界条件等诸多因素的影响。探讨了以上每个因素及其对模型误差所造成的影响。     

有限元技术在心动脉支架设计中的应用

支架植入后再狭窄是限制支架应用的主要问题,大量研究表明支架设计对于再狭窄具有较大影响.有限元技术被认为是进行支架设计成本最低,且最适合的工具,本文综述了目前有限元技术在支架领域的应用情况,并提出了支架优化设计的方向.     

眼球-眼外肌有限元模型的建立与力学分析

将有限元分析(FEA)方法运用到眼科研究中,建立了眼球和眼外肌的三维有限元模型并进行外力加载,通过非线性有限元计算过程得出模型的位移、应力、应变等结果,探讨眼部结构与受力、运动之间的关系,所得结果与眼科临床知识相符合.     

QT间期的检测与分析

心电图中的QT间期主要反映了心室复极化的时程,而QT间期的变异蕴含了心室复极变化的重要信息,对这些信息的提取和分析对研究心肌缺血、恶性心律失常等疾病有重要的意义.文中针对QT间期自动检测算法、QT离散度分析和QT变异性分析,分别介绍了它们的研究方法和研究进展,并指出了今后的发展方向.     

人体真实形状手指内的血液流动和温度分布的有限元分析

本研究的目的是要考察人体末梢的血流变化及温度调节特性. 分别对上肢大血管内血液流动及手指的传热特性进行分析并建立了数学模型.采用一维非线性脉动流体力学模型模拟大血管内的血液流动,采用描述多孔介质内流体流动的Darcy模型模拟组织内血液流动, 而用多孔介质内的能量方程描述组织内的传热特性.同时利用基于图像的建模方法,由手指的MRI系列图像建立了中指的计算机模型并生成了有限元网格.通过分析,得到人体真实形状手指内的血液流动和温度分布,并与由红外热像仪测得的结果进行了比较.比较结果显示,手指的皮肤温度变化趋势与实测结果相同,说明该模拟分析系统能够较好地分析上肢血流及末梢的传热特性.     

用有限元法对上颌总义齿塑料基托不同网状加强的效果比较

本研究采用三维有限元法,对上颌总义齿网状加强塑料基托的不同网架材料、不同加强部位、不同网孔形式,进行了应力分析比较。结果表明加强材料以钴铬合金网最强,不锈钢略次,铝合金网较次,尼龙网较差,未加强塑料基托最差。加强部位以5 5嵴顶唇颊缘包括腭部至5 5远中连线最好,7 7嵴顶唇颊缘至上腭后缘次之,3 3嵴顶唇缘至3 3远中连线较次,三者均优于仅加强于3 3、5 5、6 6嵴顶区呈弓形加强或弓形加后横杠式加强。网孔形式45°梭形孔与90°方形孔加强效果无差异。     

老年健康女性盆底肛提肌有限元模型的建立及意义

为建立老年健康女性盆底肛提肌有限元模型(FEM),对一老年未孕女性健康志愿者进行骨盆CT及MRI薄层扫描,获得其骨盆及盆底肛提肌的原始图像数据,随后应用Mimics12.0及Geomagic9.0图像处理软件将骨盆诸骨、肛提肌及其相关肌肉进行三维重建和网格优化,在Ansys11.0软件平台上构建骨盆与肛提肌群的肌骨系统FEM,并最终获得精确的老年健康女性盆底肛提肌及骨盆的FEM。结果表明:采用CT及MRI薄层扫描数据建立的FEM真实可靠,能逼真反应盆底肛提肌的空间立体解剖关系,避免了已往依赖于尸体标本解剖获得模型的缺点,所获得的模型数据更加接近于活体解剖,有利于后期的有限元分析。     

LISS钢板治疗股骨远端骨折有限元建模及分析

目的 建立LISS-DF治疗股骨远端骨折近端螺钉不同单双皮质固定的三维有限元模型,并进行初步生物力学分析.方法 提取CT图片相关数据,利用自行编写程序生成命令流文件,建立完整股骨以及16个不同LISS-DF治疗股骨远端AO分型33-A3型骨折的实体模型(钢板和股骨不接触、螺钉分别固定于钢板和股骨),进行网格划分.分析不同载荷作用下完整股骨和LISS钢板近端螺钉全双皮质固定治疗骨折的模型受力状况.结果 建立了相关的有限元模型.不同载荷作用下,LISS钢板近端螺钉全双皮质固定模型和完整股骨的应力集中均位于股骨颈内侧和股骨干外侧中下1/3处.相同载荷作用下,LISS钢板近端螺钉全双皮质固定模型的股骨颈部最大等效应力值略减小,股骨干最大等效应力值明显减小.结论 研究建立的三维有限元模型,为应用LISS治疗股骨骨折的生物力学分析提供了良好的实验平台和基础.从生物力学角度而言,LISS-DF近端螺钉全双皮质固定为治疗股骨远端复杂骨折的有效方法.     

The Use of Likelihood-Based Confidence Intervals in Genetic Models

This article describes the computation and relative merits of likelihood-based confidence intervals, compared to other measures of error in parameter estimates. Likelihood-based confidence intervals have the advantage of being asymmetric, which is often the case with structural equation models for genetically informative studies. We show how the package Mx provides confidence intervals for parameters and functions of parameters in the context of a simple additive genetic, common, and specific environment threshold model for binary data. Previously published contingency tables for major depression in adult female twins are used for illustration. The support for the model shows a marked skew as the additive genetic parameter is systematically varied from zero to one. The impact of allowing different prevalence rates in MZ vs. DZ twins is explored by fitting a model with separate threshold parameters and comparing the confidence intervals. Despite the improvement in fit of the different prevalences model, the confidence intervals on all parameters broaden, owing to their covariance.     

The Response of Cranial Biomechanical Finite Element Models to Variations in Mesh Density

Finite element (FE) models provide discrete solutions to continuous problems. Therefore, to arrive at the correct solution, it is vital to ensure that FE models contain a sufficient number of elements to fully resolve all the detail encountered in a continuum structure. Mesh convergence testing is the process of comparing successively finer meshes to identify the point of diminishing returns; where increasing resolution has marginal effects on results and further detail would become costly and unnecessary. Historically, convergence has not been considered in most CT‐based biomechanical reconstructions involving complex geometries like the skull, as generating such models has been prohibitively time‐consuming. To assess how mesh convergence influences results, 18 increasingly refined CT‐based models of a domestic pig skull were compared to identify the point of convergence for strain and displacement, using both linear and quadratic tetrahedral elements. Not all regions of the skull converged at the same rate, and unexpectedly, areas of high strain converged faster than low‐strain regions. Linear models were slightly stiffer than their quadratic counterparts, but did not converge less rapidly. As expected, insufficiently dense models underestimated strain and displacement, and failed to resolve strain “hot‐spots” notable in contour plots. In addition to quantitative differences, visual assessments of such plots often inform conclusions drawn in many comparative studies, highlighting that mesh convergence should be performed on all finite element models before further analysis takes place. Anat Rec, 2011. © 2011 Wiley‐Liss, Inc.     

Incorporating Autoregulatory Mechanisms of the Cardiovascular System in Three-Dimensional Finite Element Models of Arterial Blood Flow

The cardiovascular system is a closed-loop system in which billions of vessels interact with each other, and it enables the control of the systemic arterial pressure and varying organ flow through autoregulatory mechanisms. In this study, we describe the development of mathematical models of autoregulatory mechanisms for systemic arterial pressure and coronary flow and discuss the connection of these models to a hybrid numerical/analytic closed-loop model of the cardiovascular system. The closed-loop model consists of two lumped parameter heart models representing the left and right sides of the heart, a three-dimensional finite element model of the aorta with coronary arteries, three-element Windkessel models and lumped parameter coronary vascular models that represent the systemic circulation, and a three-element Windkessel model to approximate the pulmonary circulation. Using the connection between the systemic arterial pressure and coronary flow regulation systems, and the hybrid closed-loop model, we studied how the heart, coronary vascular beds, and arterial system respond to physiologic changes during light exercise and showed that these models can realistically simulate temporal behaviors of the heart, coronary vascular beds, and arterial system during exercise of healthy subjects. These models can be used to study temporal changes occurring in the heart, coronary vascular beds, and arterial system during cardiovascular intervention or changes in physiological states.     

基于生物力学有限元法的足跟痛发生与康复机制

目的 研究足跟痛病症的发生与康复机制,为临床上足跟痛治疗方法的有效性提供理论依据。方法 对足跟痛患者足膝部CT、MRI影像数据进行三维重建,建立患者足膝部的骨骼-肌肉复合有限元模型。基于所建模型采用有限元方法,仿真模拟小腿肌肉挛缩对足踝部生物力学性能的影响。结果 在小腿肌肉提升力的作用下,足底压力从足跟区向足掌区转移,且不同肌肉作用力组合方案对压力分布不产生明显差异。足底筋膜张力升高,跟骨表面产生应力集中。在240 N作用力下,跟腱附着位置和跟骨结节处产生应力峰值,分别高达10.82、11.2 MPa。结论 小腿部肌肉和跟腱中产生应力集中,会导致足踝部生物力学特性发生变化,引发足跟部疼痛。释放集中应力恢复踝关节中各骨骼和关节的位置,从而改善整体生物力学环境的方法是治疗足跟痛的康复机制。     

Finite Element Modeling of Diffusion and Partitioning in Biological Systems: The Infinite Composite Medium Problem

Four methods are proposed for modeling diffusion in heterogeneous media where diffusion and partition coefficients take on differing values in each subregion. The exercise was conducted to validate finite element modeling (FEM) procedures in anticipation of modeling drug diffusion with regional partitioning into ocular tissue, though the approach can be useful for other organs, or for modeling diffusion in laminate devices. Partitioning creates a discontinuous value in the dependent variable (concentration) at an intertissue boundary that is not easily handled by available general-purpose FEM codes, which allow for only one value at each node. The discontinuity is handled using a transformation on the dependent variable based upon the region-specific partition coefficient. Methods were evaluated by their ability to reproduce a known exact result, for the problem of the infinite composite medium (Crank, J. The Mathematics of Diffusion, 2nd ed. New York: Oxford University Press, 1975, pp. 38–39.). The most physically intuitive method is based upon the concept of chemical potential, which is continuous across an interphase boundary (method III). This method makes the equation of the dependent variable highly nonlinear. This can be linearized easily by a change of variables (method IV). Results are also given for a one-dimensional problem simulating bolus injection into the vitreous, predicting time disposition of drug in vitreous and retina. © 2000 Biomedical Engineering Society. PAC00: 8710+e, 0270Dh, 4266Ew     

The Global Impact of Sutures Assessed in a Finite Element Model of a Macaque Cranium

The biomechanical significance of cranial sutures in primates is an open question because their global impact is unclear, and their material properties are difficult to measure. In this study, eight suture‐bone functional units representing eight facial sutures were created in a finite element model of a monkey cranium. All the sutures were assumed to have identical isotropic linear elastic material behavior that varied in different modeling experiments, representing either fused or unfused sutures. The values of elastic moduli employed in these trials ranged over several orders of magnitude. Each model was evaluated under incisor, premolar, and molar biting conditions. Results demonstrate that skulls with unfused sutures permitted more deformations and experienced higher total strain energy. However, strain patterns remained relatively unaffected away from the suture sites, and bite reaction force was likewise barely affected. These findings suggest that suture elasticity does not substantially alter load paths through the macaque skull or its underlying rigid body kinematics. An implication is that, for the purposes of finite element analysis, omitting or fusing sutures is a reasonable modeling approximation for skulls with small suture volume fraction if the research objective is to observe general patterns of craniofacial biomechanics under static loading conditions. The manner in which suture morphology and ossification affect the mechanical integrity of skulls and their ontogeny and evolution awaits further investigation, and their viscoelastic properties call for dynamic simulations. Anat Rec 293:1477–1491, 2010. © 2010 Wiley‐Liss, Inc.     

上颌骨种植体与天然牙三维有限元模型的建立

探讨获得种植体与天然牙在上颌骨复合体三维影像以建立三维有限元模型的方法。采用螺旋CT断层扫描技术,数字影像与转录技术,自编程序与ANSYS软件相结合,将CT扫描图像转换为可用于有限元建模的数值图像。结果表明:三维有限元实体模型与螺旋CT三维重建影像比较,几何相似性与还原性良好,材料构造合理。说明采用螺旋CT扫描技术及ANSYS软件,建立上颌骨种植体模型切实可行,结果令人满意。     

The Establishment and Development of Finite Element Model of Human Cervical Vertebra and Its Application Example

The incidence rate of cervical spondylosis is high, and due to the complicacy of cervical vertebra structure, irregularity of shapes and non-uniformity of components, sometimes it＇ s difficult to achieve planned objectives by experiments in vitro through stress and strain analysis. Besides, the biomechanical factors are of vital significance in the cause of spinal disorders. In this paper the author makes a summary of the present modeling of human cervical vertebra and describes the major methods of establishing the finite element model of human cervical vertebra through several self-constructed models. With the advance of computer technology, the finite element methods have been rapidly developed in cervical vertebra biomechanical researches and have became a major approach for biomechanical researches to simulate more and more clinical conditions.     

The Use of Alternative Methods in Reducing Menopausal Complaints in Turkey

Background

Millions of women experience menopause every year, therefore the aim of this study is to determine the rates of application of alternative methods applied by women in order to reduce their complaints caused by menopause and alternative application methods.

Materials and Methods

This study was carried out on 246 women in their menopausal period. The data was obtained by the researcher through face to face interviews during the home visits. During the collection of data, a questionnaire form by the researcher that was developed in accordance with the literature information was applied.

Results

37.4% of women were determined to use alternative methods to reduce their menopausal symptoms. In the consequence of statistical analysis, a significant relation was found between the menopausal complaints such as hot flashes, night sweats and sleeping problem and the use of alternative methods in order to reduce their menopausal complaints (p<0.05).

Conclusion

It was determined that the women at their menopausal ages experienced vasomotor complaints and sleeping problems and they used alternative methods to reduce those problems.