侧向冲击载荷作用下髋护具对股骨-骨盆复合体生物力学响应的影响

目的利用三维有限元法研究髋部护具对人体股骨-骨盆复合体在侧向冲击载荷作用下生物力学响应的影响。方法基于中国力学虚拟人模型库建立股骨-骨盆-软组织复合体的三维有限元模型,包括皮质骨、松质骨和软组织,并在此基础上建立髋部护具和股骨-骨盆-软组织复合体系统的三维有限元模型;同时,在两个模型中构建刚体平面仿真地面。约束地面刚体,对两个模型均施加侧向2 m/s的速度载荷,整个仿真分析时间设定为20 ms。通过三维有限元分析计算获得两模型受侧向冲击载荷过程中应力、应变变化特性,对比分析髋部护具对股骨-骨盆复合体生物力学响应的影响。结果髋部护具使股骨-骨盆复合体在侧向冲击载荷作用下的应力峰值出现时间提前4 ms以上,且应力应变水平出现大幅度降低;皮质骨上的应力峰值降低67.88%以上,松质骨上的峰值应力下降69.34%以上,松质骨上的压缩主应变峰值降低可达63%。结论在侧向冲击载荷作用下,髋部护具对股骨-骨盆复合体具有良好的保护作用,能够有效预防骨折的发生或降低骨折风险。     

正常髋部与佩戴保护支具髋部的有限元对比分析

背景：有限元法因其具有不受样本量限制,实验误差小,重复性好等优点而成为防滑倒生物力学研究的重要手段。 目的：建立正常骨盆以及佩戴护具骨盆的三维有限元模型,分析滑倒过程中骨盆各部位的应力、应变和位移分布,验证护具的有效性。 方法：以中国数字人原始资料应用Abaqus 6.51软件构建正常骨盆以及佩戴护具骨盆的三维有限元模型,固定约束地面刚体,对整个骨盆模型加载2 m/s的速度载荷,程序运算后观测骨盆模型佩戴护具前后的应力、应变及位移随时间的变化规律和分布云图。 结果与结论：与未佩戴护具比较,佩戴护具时滑倒过程中骨盆与地面的接触力、骨盆与地面产生最大接触力时松质骨最大压缩应变、大转子以及股骨颈周围应变最大值、大转子和股骨颈附近的最大von-Mises应力值、大转子和股骨颈处的平均应力值等均明显减小。提示髋部保护支具对大转子具有保护作用,能有效降低人体滑倒时转子间骨折的发生率。     

冲击条件下骨盆动脉损伤有限元模型的建立及验证

目的 构建并验证含动脉的骨盆-股骨-软组织复合体的三维有限元模型,研究骨盆动脉在侧向冲击条件下的力学响应。方法 基于1名女性志愿者的骨盆CT图像,建立骨盆及其动脉的三维有限元模型,包括骨、动脉、周围软组织以及骶髂关节、髋关节和耻骨联合等骨盆关节软骨和韧带。采用线弹性实体单元模拟骨骼,采用非线性的弹性连接单元模拟韧带,软组织包括软骨、包裹软组织和动脉等采用超弹性材料和实体单元仿真。以22.1 kg的冲击质量,3.13和5 m/s的冲击速度对坐位下的复合体进行侧面碰撞,记录模型的输出。结果 计算结果与文献报道的实验结果一致。3.31和5 m/s冲击速度下动脉的最大等效应力分别为98和216 kPa,最大拉伸应变为14.9%和20%,但不至于导致动脉断裂。结论 所建立的骨盆-股骨-软组织复合模型可用于冲击载荷下骨盆动脉的动态响应和损伤分析,为预测动脉损伤程度提供生物力学依据。     

基于显微磁共振成像和有限元分析的股骨近端微观力学行为研究

目的 本研究利用高分辨率显微磁共振成像（micro-magnetic resonance imaging,μMRI）在呈现骨微结构方面的优势和对人体无辐射的优点,结合有限元分析（finite element analysis,FEA）,无创探究人体在自然站立状态下股骨近端微观力学行为,明确股骨易骨折危险区域,为μMRI-FEA未来临床应用提供理论基础。方法 采集5例年龄55～63岁女性志愿者（58.4岁±3.4岁）的股骨近端μMRI图像。将图像中骨骼和软组织分割,三维重建得到包含股骨近端皮质骨和松质骨微结构的大尺度三维有限元模型（约一千万六面体单元）,赋予非均匀材料属性。模拟人体自然站立时股骨的受力,将其远端固定,在股骨头部位施加压缩载荷,进行线弹性有限元分析,得到股骨近端的应力和应变分布,并选取股骨颈和大转子部位10 mm~3松质骨感兴趣区域进行比较。结果 人体自然站立姿态下,股骨颈上、下侧皮质骨分别出现拉、压应力集中现象。股骨颈松质骨感兴趣区域在上下（superior-inferior,SI）、内外（medial-lateral,ML）和前后（anterior-posterior,AP）三个方向上的正应力（σ_(SI)、σ_(ML)、σ_(AP)）分别为大转子部位的13.4倍、2.2倍和1.9倍;正应变（ε_(SI)、ε_(ML)、ε_(AP)）分别为大转子部位的7.4倍、5.0倍和4.0倍。结论自然站立时股骨颈皮质骨和松质骨所受应力和应变较大,提示股骨颈是易发生骨折的高危区域,与临床观察一致。本研究为μMRI-FEA未来应用于临床无创评估股骨骨折风险进而鉴别骨折高风险人群提供了一定的前期理论支撑。     

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.     

股骨近端溶骨性转移瘤三维有限元模型的力学分析

背景：如何评估股骨近端转移瘤的骨折风险在临床上争议较多。 目的：建立股骨近端不同大小溶骨性转移瘤的三维有限元模型,分析在慢步行走过程中病变局部的应力变化,评估骨折风险。 方法：对志愿者双下肢进行薄层CT扫描获得股骨数据,图像处理软件Mimics11.1进行图像处理后数据导入建模软件UG4.0建立股骨近端3个部位溶骨性病变模型,给予加载缓慢行走时单足落地状态下股骨的载荷,利用有限元软件分析股骨颈区,转子间区及转子下区应力的变化。 结果与结论：①股骨颈水平：皮质完整的髓内缺损破坏直径至相应冠状面直径的90%局部应力突然增长至135.98 MPa,破坏一半内侧皮质的髓内病变至70%局部应力突然增长至92.34 MPa,完全破坏皮质的半球形病变至60%时,局部应力大于屈服应力,增长至101.19 MPa。②转子间水平：内侧皮质完整的髓内球形病变破坏直径至80%局部应力突然增长至131.21 MPa,破坏一半内侧皮质的髓内病变破坏至80%局部应力突然增长至105.19 MPa,完全破坏皮质的半球形病变至70%时,局部应力大于屈服应力,增长至92.21 MPa。③转子下水平：破坏一半内侧皮质的髓内病变破坏至80%局部应力突然增长至92.42 MPa,完全破坏皮质的半球形病变至70%-80%之间,局部应力增长至89.97-105.19 MPa,大于屈服应力。结果表明股骨近端未穿透骨皮质的髓内病变对股骨近端应力变化影响不大。对于破坏单侧骨皮质的病变,在股骨颈水平破坏直径大于60%时存在骨折风险,转子间水平破坏直径大于70%时存在骨折风险,转子下水平破坏直径大于70%时存在骨折风险。     

椎弓根螺钉长度变化对螺钉-骨复合体模型 应力影响的三维有限元分析研究

目的 利用三维有限元模型研究椎弓根螺钉长度变化对生理载荷下螺钉骨复合体模型的应用影响。方法 建立椎弓根螺钉和L1椎体的三维模型,并对其进行网格划分,设置椎弓根钉长度尺寸的变化范围。模拟生理载荷条件下,对不同长度尺寸的椎弓根钉有限元模型进行应力分析。结果椎弓根螺钉长度在30～50 mm范围内变化时,随着螺钉长度的增大,螺钉骨复合体模型的骨质部分承担的应力均减小,而螺钉承担的应力则增加。螺钉最大平均主应变出现在螺钉的尾端,皮质骨发生的最大平均主应力位置出现在螺钉与皮质骨接触面两侧,松质骨发生的最大平均主应力位置出现在螺钉头部与松质骨接触面两侧。当螺钉长度达到50 mm时,载荷力传递到皮质骨和松质骨分别减小了43.1%和42.3%,而螺钉上出现的则增加了38%。当椎弓根螺钉长度大于45 mm时,螺钉骨复合体模型各部分应力变化不明显。结论 椎弓根螺钉长度在30～50 mm范围变化时,在生理载荷下,椎弓根螺钉长度的增大有利于改善螺钉、皮质骨及松质骨上轴向应力的力学分布;只要骨量允许,临床选择椎弓根螺钉的长度应不小于45 mm。     

压配型髋臼假体置换后骨性髋臼的微有限元分析

目的探讨压配型髋臼假体置换术后骨性髋臼皮质骨和松质骨的骨小梁应力分布模式及松质骨是否参与承载负荷。方法应用显微CT扫描骨性髋臼的骨小梁,建立骨性髋臼的三维微有限元模型。计算压配型髋臼假体置换后骨性髋臼骨小梁的应力和应变,分析骨性髋臼骨小梁应力、应变的生物力学特征。结果当压配型金属髋臼假体植入髋臼后,骨性髋臼外表面的最高应力区位于耻骨区,最高应力为1.389 MPa。在臼顶区,高应力区的面积最大。在骨性髋臼内部的松质骨,高应力区主要分布在臼顶区,分布区域相对较广。当施加1.372 k N载荷后,骨性髋臼外表面面积较大高应力区位于臼顶区域和耻骨区域,臼顶区的最高拉应力为0.604 MPa,耻骨区骨小梁出现微损伤。在骨性髋臼内部的松质骨,面积较大高应力区主要分布在臼顶区和耻骨区。结论高应力区沿着骨性髋臼外表面呈现3点式环形分布,集中分布于耻骨区、坐骨区、臼顶区;髋臼内部松质骨骨小梁通过形变导致应力分布更加均匀。髋臼松质骨具有承受载荷功能。     

不同形状种植体支持单端固定桥的三维有限元分析北大核心

背景:种植体的形状影响其生物力学表现,目前对种植支持式单端固定桥的研究多在相同形状种植体进行,对不同形状种植体支持的单端固定桥的比较分析较少。目的:利用三维有限元建模,分析圆柱形、锥形与膨胀式3种种植体支持的单端固定桥在下颌后牙区的生物力学特征。方法:分别建立圆柱形、锥形与膨胀式种植体支持单端固定桥及其支持组织的三维有限元模型,对单端固定桥轴向90°和颊舌向45°分别施加300 N的力,分析皮质骨、松质骨的von Mises应力及种植体-基台复合体的最大位移。结果与结论:①在轴向和颊舌向加载力下,3种模型皮质骨的最大应力峰值远大于松质骨,皮质骨的最大应力峰值均集中于近悬臂种植体远中颈部周围;②膨胀式种植体模型在皮质骨中的最大von Mises应力值最低,在轴向加载力下尤其明显,在松质骨中的von Mises应力值最高;③与轴向加载力比较,颊舌向加载力下3种模型皮质骨、松质骨的von Mises应力峰值及种植体-基台复合体最大位移均增大;在颊舌向加载力下,膨胀式种植体模型的种植体-基台复合体最大位移最小;④结果表明,膨胀式种植体支持的单端固定桥稳定性最好。     

动力髋联合空心钉与动力髋联合内侧板治疗PauwelsⅢ型股骨颈骨折的有限元分析比较

目的探究动力髋螺钉(DHS)的两种手术方式(DHS联合空心钉和DHS联合股骨颈内侧板)治疗PauwelsⅢ型股骨颈骨折的生物力学优缺点。方法建立采用3种内固定方法治疗PauwelsⅢ型股骨颈骨折的有限元模型。分别为单独使用DHS内固定、DHS联合空心钉固定、DHS联合股骨颈内侧板固定,并建立正常股骨模型用于与前3个模型对比分析。在相同边界及载荷条件下比较以下结果:4个模型的股骨颈内侧(股骨头下缘至股骨距到小转子的位置)的等效应力分布;3个内固定模型的内固定物的最大等效应力值;4个模型股骨头断端最大位移。结果股骨颈内侧等效应力分布最接近正常股骨的模型是DHS联合股骨颈内侧板,单纯DHS固定的模型和DHS联合空心钉固定的模型在股骨颈内侧的等效应力集中值大于正常股骨模型,分别为53.57 MPa和26.72 MPa。股骨头骨折断端总位移:单纯DHS固定模型的位移是4.01 mm,DHS联合空心钉固定模型的位移是1.73 mm,DHS联合股骨颈内侧板固定模型的位移是1.68 mm。DHS内固定物最大等效应力由大到小分别是:单独DHS固定为101.07 MPa,DHS联合空心钉固定为38.19 MPa,DHS联合股骨颈内侧板固定为22.69 MPa。结论DHS联合空心钉与DHS联合内侧板手术方式都优于单独DHS固定的手术方式。DHS联合空心钉固定能在股骨头位移相对较小的情况下维持较高的股骨颈应力,适合于股骨颈内侧相对完整及未出现粉碎骨折的患者;DHS联合内侧板可以更好地重建股骨力线,更适合于股骨颈内侧皮质处有粉碎骨折的患者。     

Simulation of hip fracture in sideways fall using a 3D finite element model of pelvis-femur-soft tissue complex with simplified representation of whole body

Hip fractures due to sideways falls are a worldwide health problem, especially among the elderly population. The objective of this study was to simulate a real life sideways fall leading to hip fracture. To achieve this a computed tomography (CT) scan based three-dimensional (3D) finite element (FE) model of the pelvis–femur complex was developed using a wide range of mechanical properties in the bone of the complex. For impact absorption through large deformation, surrounding soft tissue was also included in the FE model from CT scan data. To incorporate the inertia effect, the whole body was represented by a spring-mass-dashpot system. For trochanteric soft tissue thickness of 14 mm, body weight of 77.47 kg and average hip impact velocity of 3.17 m/s, this detailed FE model could approximately simulate a sideways fall configuration and examine femoral fracture situation. At the contact surface, the peak impact load was 8331 N. In spite of the presence of 14 mm thick trochanteric soft tissue, within the trochanteric zone the most compressive peak principal strain was 3.5% which exceeds ultimate compressive strain. The modeled trochanteric fracture was consistent with clinical findings and with the findings of previous studies. Further, this detailed FE model may be used to find the effect of trochanteric soft tissue thickness variations on peak impact force, peak strain in sideways fall, and to simulate automobile side impact and backward fall situations.     

Validation of a finite element model of a unilateral external fixator in a rabbit tibia defect model

In case of large segmental defects in load-bearing bones, an external fixator is used to provide mechanical stability to the defect site. The overall stiffness of the bone–fixator system is determined not only by the fixator design but also by the way the fixator is mounted to the bone. This stiffness is an important factor as it will influence the biomechanical environment to which tissue engineering scaffolds and regenerating tissues are exposed. A finite element (FE) model can be used to predict the system stiffness. The goal of this study is to develop and validate a 3D anatomical FE model of a bone–fixator system which includes a previously developed unilateral external fixator for a large segmental defect model in the rabbit tibia. It was hypothesized that the contact interfaces between bone and fixator screws play a major role for the prediction of the stiffness. In vitro mechanical testing was performed in order to measure the axial stiffness of cortical bone from mid-shaft rabbit tibiae and of the tibia–fixator system, as well as the bending stiffness of individual fixator screws, inserted in bone. μCT-based case-specific FE models of cortical bone and SCREW–BONE specimens were created to simulate the corresponding mechanical test set-ups. The Young's modulus of rabbit cortical bone as well as appropriate screw–bone contact settings were derived from those FE models. We then used the derived settings in an FE model of the tibia–fixator system. The difference between the FE predicted and measured axial stiffness of the tibia–fixator system was reduced from 117.93% to 7.85% by applying appropriate screw–bone contact settings. In conclusion, this study shows the importance of screw–bone contact settings for an accurate fixator stiffness prediction. The validated FE model can further be used as a tool for virtual mechanical testing in the design phase of new tissue engineering scaffolds and/or novel patient-specific external fixation devices.     

Tissue differentiation and bone regeneration in an osteotomized mandible: a computational analysis of the latency period

Mandibular symphyseal distraction osteogenesis is a common clinical procedure to modify the geometrical shape of the mandible for correcting problems of dental overcrowding and arch shrinkage. In spite of consolidated clinical use, questions remain concerning the optimal latency period and the influence of mastication loading on osteogenesis within the callus prior to the first distraction of the mandible. This work utilized a mechano-regulation model to assess bone regeneration within the callus of an osteotomized mandible. A 3D model of the mandible was reconstructed from CT scan data and meshed using poroelastic finite elements (FE). The stimulus regulating tissue differentiation within the callus was hypothesized to be a function of the strain and fluid flow computed by the FE model. This model was then used to analyse tissue differentiation during a 15-day latency period, defined as the time between the day of the osteotomy and the day when the first distraction is given to the device. The following predictions are made: (1) the mastication forces generated during the latency period support osteogenesis in certain regions of the callus, and that during the latency period the percentage of progenitor cells differentiating into osteoblasts increases; (2) reducing the mastication load by 70% during the latency period increases the number of progenitor cells differentiating into osteoblasts; (3) the stiffness of new tissue increases at a slower rate on the side of bone callus next to the occlusion of the mandibular ramus which could cause asymmetries in the bone tissue formation with respect to the middle sagittal plane. Although the model predicts that the mastication loading generates such asymmetries, their effects on the spatial distribution of callus mechanical properties are insignificant for typical latency periods used clinically. It is also predicted that a latency period of longer than a week will increase the risk of premature bone union across the callus.     

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。     

Validation of a finite element model of the human metacarpal

Implant loosening and mechanical failure of components are frequently reported following metacarpophalangeal (MCP) joint replacement. Studies of the mechanical environment of the MCP implant-bone construct are rare. The objective of this study was to evaluate the predictive ability of a finite element model of the intact second human metacarpal to provide a validated baseline for further mechanical studies. A right index human metacarpal was subjected to torsion and combined axial/bending loading using strain gauge (SG) and 3D finite element (FE) analysis. Four different representations of bone material properties were considered. Regression analyses were performed comparing maximum and minimum principal surface strains taken from the SG and FE models. Regression slopes close to unity and high correlation coefficients were found when the diaphyseal cortical shell was modelled as anisotropic and cancellous bone properties were derived from quantitative computed tomography. The inclusion of anisotropy for cortical bone was strongly influential in producing high model validity whereas variation in methods of assigning stiffness to cancellous bone had only a minor influence. The validated FE model provides a tool for future investigations of current and novel MCP joint prostheses.     

个性化全骨盆三维有限元建模及骶髂关节骨折脱位模拟

目的建立高度仿真的个性化的完整骨盆三维有限元模型,并在此基础上进行骶髂关节骨折脱位的模拟。方法从CT精确重建独立的左、右髋骨和骶骨实体模型,根据髋骨和骶骨的外形特征,利用专门的流线型生物力学有限元网格划分器生成规则的体网格模型,并进一步建立骶髂关节的终板、软骨、关节接触面,和骨盆上的主要韧带组织及耻骨间盘。在建立的完整模型上去掉一侧的骶髂关节韧带群进行骨折脱位模拟,并与正常的情况进行对比。结果建立了高精度的个性化全骨盆的三维有限元模型,包括左右髋骨和骶骨的皮质骨、松质骨,骶髂关节的终板、软骨和带摩擦的关节接触面,韧带包括骶髂骨间韧带、骶髂前韧带、骶髂后韧带、骶棘韧带、骶结节韧带、耻骨上韧带和耻骨弓状韧带,以及耻骨间盘。正常模型的加载模拟和骶髂关节骨折脱位模拟的预测结果均与文献试验生物力学结果相符合。结论利用专门的生物力学有限元建模工具能建立更复杂更精确的三维有限元模型,成为全骨盆生物力学分析研究的平台和基础。     

Establishment of an architecture-specific experimental validation approach for finite element modeling of bone by rapid prototyping and high resolution computed tomography

A new experimental validation method for assessing the accuracy of large-scale finite element (FE) models of bone micro-structure at the apparent and tissue level was developed. Augmented scaled bone replicas were built using rapid prototype machines based on micro-computed tomography (micro-CT) data. The geometric accuracy of the model was evaluated by comparing experimental tests with the replicas to the FE solution based on the same micro-CT data. A new version of the large-scale FE solver was developed to incorporate orthotropic material properties, hence the experimentally determined properties of the rapid prototype material were input into the FE models. The modified FE solver predicted the experimental apparent level stiffness within less than 1%, and the difference between experimental strain gauge measurements and FE-calculated surface stresses was 7% and 49% on a flat and curved surface region, respectively. While absolute error estimates of surface stresses were limited due to strain gauge errors, the relatively larger difference on the curved surface is indicative of the limitations of a hexahedron FE model for representing such geometries. Although the validation approach is applied here for hexahedron based meshes, the method is flexible for varying bone architectures and will be important for validation of future large-scale FE modeling developments that utilize techniques such as mesh smoothing and tetrahedron elements.