Improved prediction of proximal femoral fracture load using nonlinear finite element models.

Hip fracture, which is often due to osteoporosis or other conditions affecting bone strength, can lead to permanent disability, pneumonia, pulmonary embolism, and/or death. Great effort has been directed toward developing noninvasive methods for evaluating proximal femoral strength (fracture load), with the goal of assessing fracture risk. Previously, computed tomographic scan-based, linear finite element (FE) models were used to estimate proximal femoral fracture loads ex vivo in two load configurations, one approximating joint loading during single-limb stance and the other simulating impact from a fall. Measured and computed fracture loads were correlated (stance, r=0.867; fall, r=0.949). However, precision for the stance configuration was insufficient to identify subjects with below average fracture loads reliably. The present study examined whether, for this configuration, nonlinear FE models could be used to identify these subjects. These models were found to predict fracture load within +/-2.0 kN (r=0.962). This level of precision is sufficient to identify 97.5% of femora with fracture loads 1.3 standard deviations below the mean as having below average fracture loads. Accordingly, 20% of subjects with below average fracture loads, i.e. those with the lowest fracture loads and likely to be at greatest risk of fracture, would be correctly identified with at least 97.5% reliability. This FE modeling method will be a powerful tool for studies of hip fracture.     

3D Finite Element Analysis of a Man Hip Joint Femur under Impact Loads

Objective： The biomechanical characters of the bone fracture of the man femoral hip joint under impact loads are explored. Methods ：A biosystem model of the man femoral hip joint by using the GE （ General Electric） lightspeed multi-lay spiral CT is conducted. A 3D finite element model is established by employing the finite element software ANSYS. The FE analysis mainly concentrates on the effects of the impact directions arising from intense movements and the parenchyma on the femoral hip joint on the stress distributions of the proximal femur. Results：The parenchyma on the hip joint has relatively large relaxation effect on the impact loads. Conclusion：Effects of the angle δ of the impact load to the anterior direction and the angle γ of the impact load to the femur shaft on the bone fracture are given;δ has larger effect on the stress and strain distributions than the angle γ,which mainly represents the fracture of the upper femur including the femoral neck fracture when the posterolateral femur is impacted, consistent with the clinical resuits.     

Development of a hybrid finite element model for individual simulation of intertrochanteric osteotomies.

Intertrochanteric osteotomies of the proximal femur are used to improve the anatomy and function of the hip joint in a number of orthopaedic diseases. To investigate the geometrical and biomechanical aspects of pre-operative planning we created a set of programs to automatically perform a simulation of intertrochanteric osteotomies on a three-dimensional finite element model of the human proximal femur based on computed tomography (CT) data and using uniform brick-shaped elements. To eliminate artefacts resulting from the rough surface of the brick elements, the femoral head was represented by a tetrahedron-based head that included a cartilage layer and a subchondral cortical zone. Applicability of the procedure was tested by performing a parametric study using a model created from CT scans taken in vivo, by applying individually calculated force conditions for the one-leg stance situation. We found a large influence of osteotomy angle on the observed stress in the femoral head cartilage, especially in a situation with insufficient containment of the femoral head. The model presented here is a biomechanical tool to simulate intertrochanteric osteotomies patient-specifically for a better understanding of the effects of such operations in the individual case. The open design of the described programs allows future interfacing with surgical navigation and robot systems.     

A Robust 3D Finite Element Simulation of Human Proximal Femur Progressive Fracture Under Stance Load with Experimental Validation

Clinical implementation of quantitative computed tomography-based finite element analysis (QCT/FEA) of proximal femur (hip) fractures requires (i) to develop a bone material behavior able to describe the progressive fracturing process until complete failure of the hip. And (ii) to validate the model with realistic test data that represent typical hip fractures. The objective of the current study was to develop and experimentally validate an accurate 3D finite element (FE) model coupled to a quasi-brittle damage law to simulate human proximal femur fracture considering the initiation and progressive propagation of multiple cracks phases under quasi-static load. The model is based on continuum damage mechanics that can predict hip fracture in more adequate physical terms than criteria-based fracture models. In order to validate the model, ten human proximal femurs were tested until complete fracture under one-legged stance quasi-static load. QCT/FE models were generated and FE simulations were performed on these femurs with the same applied loads and boundary conditions than in the stance experiments. The proposed FE model leads to excellent agreement (R ² = 0.9432) between predicted and measured results concerning the shape of the force–displacement curve (yielding and fracturing) and the profile of the fractured edge. The motivation of this work was to propose a FE model for possible clinical use with a good compromise between complexity and capability of the simulation.     

Prediction of fracture location in the proximal femur using finite element models.

Finite element (FE) models of the proximal femur are often used to study hip fracture. To interpret the results of these models, it is important to know whether the models accurately predict fracture location and/or type. This study evaluated the ability of automatically generated, CT scan-based linear FE models of the proximal femur to predict fracture location and fracture type. Fracture location was defined as the specific location of the fracture. Fracture type was a categorical variable defined as either a cervical or a trochanteric fracture. FE modeling and mechanical testing of 18 pairs of human femora were performed under two loading conditions, one similar to joint loading during single-limb stance and one simulating impact from a fall. For the stance condition, the predicted and actual fracture locations agreed in 13 of the 18 cases (72% agreement). For the fall condition, the predicted and actual fracture locations agreed in 10 of the 15 cases where the actual fractures could be identified (67% agreement). The FE models correctly predicted that only cervical fractures occurred in the stance configuration. For the fall configuration, FE-predicted and actual fracture types agreed in 11 of the 14 cases that could be compared (9 trochanteric, 2 cervical; 79% agreement). These results provide evidence that CT scan-based FE models of the proximal femur can predict fracture location and fracture type with moderate accuracy.     

An experimental method for the application of lateral muscle loading and its effect on femoral strain distributions

Experimental models that have been used to evaluate hip loading and the effect of hip implants on bone often use only a head load and abductor load. Anatomic considerations and in vivo measurements have lead several investigators to suggest that these models are inaccurate because they do not incorporate the loads imposed by additional muscles. The aim of this study was to evaluate the strains in the proximal and mid diaphysis of the femur for five hip loading models, one with a head load and abductor load only and four which incorporated lateral muscle loads as well. Head load to body weight load ratios were used to evaluate the physiologic accuracy of these models and strains were compared to determine the extent of strain changes as a function of model complexity. All models which incorporated additional lateral muscle loads more accurately simulated head load to body-weight load ratios than the simple abductor-only model. The model which incorporated a coupled vastus lateralis and iliotibial band load in addition to the abductor load provided the simplest configuration with a reasonable body-weight to head-load ratio.     

有限元分析股骨颈骨折伴下后方不同程度骨缺损空心螺钉内固定后的稳定性

文题释义：有限元分析：是基于结构力学分析迅速发展起来的一种现代计算方法,通过计算机硬件及软件将载荷、形态、材料结构和力学性能较为复杂的整体划分为有限个简单的单元,进而充分反映整体内外部应力、应变、位移等力学参数的变化情况。通过将股骨近端及空心钉进行有限网格划分,施加载荷后可了解到股骨近端、空心钉每个网格的应力与应变情况。 创伤性股骨头坏死：各类因素引起股骨头血供下降或力学环境改变,导致股骨头内骨小梁坏死塌陷、髋关节疼痛及功能障碍的常见疾病。其中创伤性股骨头坏死与激素性股骨头坏死等不同,生物力学因素在其病情发生发展中发挥重要作用。骨小梁出现“损伤-微骨折-修复”交替反应,超过生理修复负荷,骨小梁修复重塑反应受阻,局部骨小梁走形杂乱无章,这是创伤性股骨头坏死重要的发病机制。 背景：空心螺钉固定为新鲜股骨颈骨折的首选治疗方法,但对于伴有骨缺损的患者,由于股骨近端力学传导及稳定性发生明显改变,易导致内固定物失效、骨折不愈合或延迟愈合等,因此生物力学研究具有重要的临床意义。 目的：利用有限元方法探究骨缺损后股骨近端的生物力学改变,比较不同构型空心螺钉固定内收型股骨颈骨折伴下后方不同程度骨缺损的生物力学效果。 方法：获取一名成年健康男性志愿者股骨近端CT扫描DICOM原始数据,利用MIMICS 10.01软件、Rhino3D NURBS软件制作内收型股骨颈骨折伴后下方不同程度骨缺损模型(无缺损模型、小缺损模型、中缺损模型与大缺损模型),在4组模型中各配置两种构型的空心螺钉(倒三角、正三角),装配完成后进行网格划分、材料属性赋值;通过ABAQUS 6.12软件建立股骨头中心和表面的耦合关系,对所有模型施加缓慢行走时的载荷和约束。 结果与结论：①无缺损模型的股骨颈内侧承受压应力,外侧承受张应力,股骨头应力分布较为均匀,随着股骨颈下后方缺损程度的增加,压力侧和张力侧空心螺钉、空心螺钉尾部及股骨头的应力峰值逐渐上升;②随着缺损程度的增加,空心螺钉压力侧应力峰值逐渐增加,在中、大缺损模型中,倒三角组高于正三角组(P < 0.05),在其余模型中两组之间无差异(P > 0.05);③随着缺损程度的增加,空心螺钉张力侧应力峰值逐渐增加,在无缺损与小缺损模型中,正三角组高于倒三角组(P < 0.05);在大缺损模型中,正三角组低于倒三角组(P < 0.05);在中缺损模型中两组无差异;④随着缺损程度的增加,股骨头应力峰值逐渐增加,3种模型中倒三角组与正三角组均无明显差异(P > 0.05);⑤随着缺损程度的增加,空心螺钉尾部应力峰值逐渐增加,在小、中、大缺损模型中,倒三角组高于正三角组(P < 0.05),在无缺损模型中两组无差异(P > 0.05);⑥结果表明,下后方不同程度骨缺损可显著影响股骨近端力学性能,对于无缺损或缺损程度较小的股骨颈骨折,空心螺钉倒三角构型的生物力学性能优于正三角构型,而对于缺损程度较大的股骨颈骨折,空心螺钉正三角构型的生物力学性能优于倒三角构型。 ORCID: 0000-0001-9190-2904(张成宝) 中国组织工程研究杂志出版内容重点：人工关节;骨植入物;脊柱;骨折;内固定;数字化骨科;组织工程     

Finite element analysis of a bone-implant system with the proximal femur nail.

Static analysis with finite element of a realistic femur nail bone-implant system in a typical proximal femoral fracture under physiological load bearing situations provides results for stress, displacement and strain. The question to be answered is, if simulation with the finite element analysis is able to explain biomechanically clinical observed patterns of failure. Surface-Reconstruction with CT database of a proximal femur and reconstruction with CT based density data was done. Next steps were to unite the bone structure with the Proximal Femoral Nail and to model two relevant fractures (31-A2.2 and A2.3 according AO). After modelling of geometry, isotropic material behaviour and load application numeric calculation of the femur-nail system with FE-software was performed. FE simulation mainly shows an axial dislocation of the femoral head screw with nearly no dislocation of the antirotation screw. This so-called z-effect therefore means: (1) Tilting of the proximal main fragment around the sagittal axis between the screws and (2) relative movement of both screws in the frontal plane. Relative movement of the two screws against each other could be the reason for implant failure, the so called cut out. Furthermore simulation shows different gliding of the screws explaining the so called z-telescoping. The analyzed stress patterns have to be relativized, because isotropic material behaviour of cancellous bone was assumed. Further examinations for this issue are necessary.     

Effect of the stiffness of bone substitutes on the biomechanical behaviour of femur for core decompression

Core decompression is the most common procedure for treatment of the early stages of osteonecrosis of the femoral head. The purpose of this study was to compare the biomechanical performance of four different bone graft substitutes combined with core decompression. Subject-specific finite element models generated from computed tomography (CT) scan data were used for a comprehensive analysis. Two different contact conditions were simulated representing states of osseointegration at the interface. Our results showed that the use of a low-stiffness bone substitute did not increase the risk of femoral fracture in the early postoperative phase, but resulted in less micromotion and interfacial stresses than high-stiffness bone substitutes.     

Comparison of an inhomogeneous orthotropic and isotropic material models used for FE analyses

Finite element (FE) analysis has been widely used to study the behaviour of bone or implants in many clinical applications. One of the main factors in analyses is the realistic behaviour of the bone model, because the behaviour of the bone is strongly dependent on a realistic bone material property assignment. The objective of this study was to compare isotropic and orthotropic inhomogeneous material models used for FE analyses of the "global" proximal femur and "small" specimens of the bone (cancellous and cortical). Our hypothesis was that realistic material property assignment (orthotropy) is very important for the FE analyses of small bone specimens, whereas in global FE analyses of the proximal femur, this assignment can be omitted, if the inhomogeneous material model was used. The three-dimensional geometry of the "global" proximal femur was reconstructed using CT scans of a cadaveric femur. This model was implemented into an FE simulation tool and various bone material properties, dependant on bone density, were assigned to each element in the models. The "small" specimens of cortical and cancellous bone were created in the same way as the model of the proximal femur. The results obtained from FE analyses support our above described hypothesis.     

The Impact of Voxel Size-Based Inaccuracies on the Mechanical Behavior of Thin Bone Structures

Computed tomography (CT)-based measures of skeletal geometry and material properties have been widely used to develop finite element (FE) models of bony structures. However, in the case of thin bone structures, the ability to develop FE models with accurate geometry derived from clinical CT data presents a challenge due to the thinness of the bone and the limited resolution of the imaging devices. The purpose of this study was to quantify the impact of voxel size on the thickness and intensity values of thin bone structure measurements and to assess the effect of voxel size on strains through FE modeling. Cortical bone thickness and material properties in five thin bone specimens were quantified at voxel sizes ranging from 16.4 to 488 μm. The measurements derived from large voxel size scans showed large increases in cortical thickness (61.9–252.2%) and large decreases in scan intensity (12.9–49.5%). Maximum principal strains from FE models generated using scans at 488 μm were decreased as compared to strains generated at 16.4 μm voxel size (8.6–64.2%). A higher level of significance was found in comparing intensity (p = 0.0001) vs. thickness (p = 0.005) to strain measurements. These findings have implications in developing methods to generate accurate FE models to predict the biomechanical behavior of thin bone structures.     

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.     

人在摔倒时股骨上端承载能力的有限元分析——(Ⅱ)摔跤姿态和载荷位置对股骨承载能力的影响研究

我们用有限元模型结合Hofftnan失效准则参数化地研究了载荷条件对股骨承载能力的影响。载荷条件包括摔跤姿态角，载荷施加位置及髋关节间的摩擦阻力。参数化研究结果表明：载荷施加位置是影响股骨承载能力的关键因素；当外载荷作用在股骨头部时，有两个股骨承载能力的低谷区，如果外载施加在这两个区域，则股骨颈极易发生骨折；髋关节间的摩擦阻力可严重地影响股骨承载能力，这对骨关节炎患者有很大的内在意义。     

骨质疏松影响股骨近端防旋髓内钉治疗股骨转子间骨折的有限元仿真

文题释义：骨质疏松：是骨量减少导致骨微结构破坏、进而易发生骨折的全身性疾病,它不仅是导致髋部骨折的重要原因之一,也是导致股骨近端防旋髓内钉内固定失效的重要原因之一。 股骨转子间骨折：在老年人中较为常见,现主要是手术治疗,股骨近端防旋髓内钉被广泛应用于临床。股骨转子间骨折内固定术后失效时有发生,其原因可能与骨质疏松、骨折类型、尖顶距值、复位质量等密切相关。 背景：股骨近端防旋髓内钉治疗股骨转子间骨折在临床应用广泛,但仍有部分术后内固定失效病例,股骨近端骨质疏松被认为是一个重要原因。Singh指数是评价股骨近端骨质疏松严重程度的一个重要指标,基于Singh指数探讨不同骨质疏松程度对股骨近端防旋髓内钉治疗转子间骨折疗效的影响,对减少内固定失效概率,增加手术成功率具有重要意义。 目的：探讨不同骨质疏松程度对股骨近端防旋髓内钉治疗转子间骨折疗效的影响,为临床治疗转子间骨折提供新思路和实验基础。 方法：选取1例左侧股骨转子间骨折患者的CT资料,导入Mimics 19.0和Geomagic studio 2017软件中进行提取、优化得到右侧股骨三维模型。运用Solidworks 2017软件画出内固定模型并与股骨模型按照标准手术技术装配,以STEP格式导入Hypermesh 14.0软件中截骨得到AO 2.1型股骨转子间骨折模型,参照Singh指数1-6划分应力骨小梁得到A-F模型,设置材料属性参数、边界条件、施加载荷,分别储存为K文件导入LS-DYNA软件求解。 结果与结论：①当股骨头受力时,Singh 6-Singh 1股骨头颈骨块中螺旋刀片产生切割,普通骨小梁消失,包裹螺旋刀片的应力骨小梁不但没有消失,且承载和分散了部分应力,使得螺旋刀片仍具有较大的接触面积和把持力,维持着骨折的复位,减少了股骨头颈骨块的内翻和旋转;②从Singh 6-Singh 1,随着应力骨小梁的消失,骨质疏松越严重,股骨近端防旋髓内钉治疗股骨转子间骨折就越容易失效;③股骨近端海绵状的丰厚骨小梁,特别是应力骨小梁,通过抵抗、缓冲弯曲应变而在维持股骨的弹性稳定起着重要作用,是股骨近端弹性稳定的重要结构。 ORCID: 0000-0002-4097-2790(黄培镇) 中国组织工程研究杂志出版内容重点：人工关节;骨植入物;脊柱;骨折;内固定;数字化骨科;组织工程     

人在摔倒时股骨上端承载能力的有限元分析——(II)摔跤姿态和载荷位置对股骨承载能力的影响研究

我们用有限元模型结合Hoffman失效准则参数化地研究了载荷条件对股骨承载能力的影响。载荷条件包括摔跤姿态角,载荷施加位置及髋关节间的摩擦阻力。参数化研究结果表明载荷施加位置是影响股骨承载能力的关键因素;当外载荷作用在股骨头部时,有两个股骨承载能力的低谷区,如果外载施加在这两个区域,则股骨颈极易发生骨折;髋关节间的摩擦阻力可严重地影响股骨承载能力,这对骨关节炎患者有很大的内在意义。     

髋部骨折的发生与股骨近端三维几何解剖形态的相关性研究

目的运用计算机辅助设计(computer aided design,CAD)及三维重建技术测量髋部几何解剖形态学参数,探究骨折人群股骨近端解剖形态与正常组人群(未骨折人群)的差异,分析其对髋部骨折发生率和发生类型的影响。方法通过髋部骨折患者正常侧下肢CT扫描图像,运用Mimics 10.01软件建立三维解剖形态模型,并测量股骨颈前倾角(femoral neck anteversion angle,FNAA)、颈干角(neck-shaft angle,NSA)、股骨头直径(femoral head diam-eter,FHD)及股骨颈轴长(length of femoral neck axis,LFNA)等正常股骨近端三维几何解剖形态学参数。结果股骨颈骨折组中FNAA、NSA、FHD、LFNA平均值为分别为(7.9±4.6)°、(128.6±4.6)°、(46.0±4.6)mm、(47.1±5.1)mm。股骨粗隆间骨折组中FNAA、NSA、FHD、LFNA平均值分别为(15.5±6.8)°、(134.7±6.9)°、(45.3±3.6)mm、(46.7±3.4)mm。股骨粗隆间骨折组FNAA及NSA无论男性还是女性都显著大于股骨颈骨折组(P<0.01),股骨颈骨折组、股骨粗隆间骨折组FNAA和NSA均与正常对照组有非常显著的差异性。结论中国人群FNAA较正常值大越容易发生股骨粗隆间骨折,较正常值小越容易发生股骨颈骨折。髋部骨折患者NSA较正常值大,其中NSA越大越容易发生股骨粗隆间骨折。骨折组人群的股骨近端解剖结构与正常人存在一定的差异,以角度解剖学参数影响为主。年龄越大越容易发生股骨粗隆间骨折,年龄越小越容易发生股骨颈骨折。     

股骨转子间骨折不同外侧壁分型髓内钉治疗的有限元分析

背景：目前针对外侧壁破损型股骨转子间骨折的手术内固定方式存在争议,以股骨近端防旋髓内钉固定为主流方案,不同外侧壁分型的股骨转子间骨折髓内固定的生物力学研究较少。目的：通过有限元分析比较股骨近端防旋髓内钉治疗不同外侧壁分型股骨转子间骨折的生物力学特点,探讨外侧壁对股骨转子间骨折内固定的影响。方法：选择1例健康老年女性患者,根据股骨近端CT扫描数据,应用Mimics 21.0,Geomagic Wrap,Creo 6.0,Abaqus 2020软件建立股骨近端和股骨近端防旋髓内钉的三维有限元模型,模拟外侧壁稳定型、危险型及破裂型股骨转子间骨折,建立股骨近端防旋髓内钉内固定装配模型。观察在静止及行走2种状况下赋予同等载荷时3种骨折内固定模型的等效应力及位移分布云图。结果与结论：(1)A3.3型股骨转子间骨折在动态载荷时最大等效应力及位移均最大,最大等效应力约为A2.3型的2倍,A1.3型的2.7倍,最大等效位移约为A2.3型的1.5倍,A1.3型的3倍,静态时各型差别不明显;(2)动静态载荷时股骨颈、骨折端及主钉处等效应力A3.3型较A1.3和A2.3型增大,以主钉处明显;(3)动态载荷时股...     

Short Term In Vivo Precision of Proximal Femoral Finite Element Modeling

As more therapies are introduced to treat osteoporosis, precise in vivo methods are needed to monitor response to therapy and to estimate the gains in bone strength that result from treatment. A method for evaluating the strength of the proximal femur was developed and its short term reproducibility, or precision, was determined in vivo. Ten volunteer subjects aged 51–62 years (mean 55.6 years), eight women and two men, were examined using a quantitative computed tomography (QCT) protocol. They were positioned, scanned, re-positioned and re-scanned. The QCT images were registered in three-dimensional space, and finite element (FE) models were generated and processed to simulate a stance phase load configuration. Stiffness was computed from each FE model, and strength was computed using a regression equation between FE stiffness and fracture load for a small set n=6 of experimental specimens. The coefficients of variation (COV) and repeatability (COR=2.23* 2*COV) were determined. The COV for the FE fracture load computed was 1.85%, and the detectable limit (coefficient of repeatability) for serial measurements was 5.85%. That is, if a change of 5.85% or more in computed FE fracture load is observed, it will be too large to be consistent with measurement variation, but instead can be interpreted as a real change in the strength of the bone. The detectable limit of this method makes it suitable for serial research studies on changes in femoral bone strength in vivo. © 2000 Biomedical Engineering Society. PAC00: 8719Rr, 8759Fm, 8710+e     

三角稳定固定系统对股骨颈骨折生物力学特性的有限元分析

目的:运用有限元分析,探讨三角稳定固定系统对股骨颈骨折的生物力学特性。方法:选取1名健康青年志愿者,获取其股骨CT影像学资料,构建股骨三维模型及股骨颈骨折三维模型。运用Ansys12.1有限元分析软件,模拟人体直立情况下正三角、倒三角稳定固定系统对内固定物应力分布、骨折处位移的影响。结果:正三角内固定、倒三角内固定模型的股骨头最大等效应力接近,倒三角内固定模型的内固定物最大等效应力低于正三角内固定。正三角内固定、倒三角内固定模型的股骨近端、内固定物最大位移接近。结论:正三角、倒三角稳定固定系统的股骨头最大等效应力、股骨近端最大位移、内固定物最大位移接近,倒三角内固定模型的内固定物最大等效应力更低。 【关键词】三角稳定固定系统;股骨颈骨折;生物力学;有限元分析     

Assessing the Susceptibility to Local Buckling at the Femoral Neck Cortex to Age-Related Bone Loss

Although it is known that long cortical bone structurally alter their area moment of inertia with age related bone loss maintaining their bending strength, the incidence of fragility fractures associated with cortical thinning still prevails. We hypothesize that cortical thinning with aging increases the local buckling susceptibility under abnormal or eccentric loads, and initiates fracture. The paper presents a series of 3D geometrical model derived from CT scans of a human femoral neck used to simulate age-related bone loss. The purpose of the model is to predict the susceptibility of local buckling at the femoral neck in falls by elderly folks. Geometric three-dimensional models of femoral neck cortices were developed from 7 human cadaver femurs (4 female, 3 male, 52–68 years). Three age related femoral neck models were simulated by either reducing (young age-related model) or increasing (old age-related model) the outer cortical surfaces in the radial-direction, by 1-mm. The control model was the middle-age related model. The inner cortex diameter was also adjusted to equilibrate the compressive stresses, based on the load-profile of a single-legged stance. Based on the old age related model, two additional “fragile” models were simulated by reducing the compressive load profile by 10 and 20% changing the inner cortex diameter, respectively. Using these models for each specimen, the consequence of a fall on the greater trochanter was evaluated. The Finite Strip Method (FSM) was used to investigate the association between local buckling at the femoral neck and the load to failure. Under constant loading, buckling progressively reduced the load to failure with aging, as seen in 2/7 of the middle age (by 9–15%) and 5/7 of the old age (by 7–32%) related models. In the fragile models, a 51% reduction in the load to failure was noted. Structural adaptation to age-related bone loss might preserves the bending strength under physiologic loads, but cortical thinning effects the buckling ratio reaching a critical threshold that would make the bone susceptible to local buckling at the femoral neck increasing the risk of fracture in a fall.