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

Study on micromechanical behavior of the proximal femur based on micro-magnetic resonance imaging and finite element analysis

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(σSI、σML、σAP)分别为大转子部位的13.4倍、2.2倍和1.9倍;正应变(εSI、εML、εAP)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。

Objective Taking the advantages of high-resolution micro magnetic resonance imaging(μMRI)on visualizing bone microstructure and having little radiation to patients,the current study usedμMRI in combination with finite element analysis(FEA)to non-invasively explore the micromechanical behavior of the human femur under standing posture in order to identify regions at high risks of femoral fractures and eventually to provide a theoretical basis for future clinical applications ofμMRI-FEA.MethodsμMRI images of the proximal femurs were obtained from 5 female volunteers aged 55-63 years(mean 58.4 years±3.4 years old).The proximal femurs were segmented out from surrounding muscles and other soft tissues in the images.Large-scale three-dimensional finite element models(about 10 million hexahedral elements),including cortical and cancellous bone microstructures,were built and assigned with inhomogeneous material properties.To simulate the loading condition of the femur for the standing posture,the distal femur was fixed and a compressive load was applied to the femoral head.Linear elastic FEA was performed to obtain the distributions of stress and strain in the proximal femur.Regions of interest of 10 mm 3 cancellous bone in the femoral neck and greater trochanter were selected for comparative analysis.Results Under the standing posture,tensile and compressive stress concentrations were observed in superior and inferior cortical bone of the femoral neck,respectively.For the cancellous regions of interest,the normal stresses along the superior-inferior(SI),medial-lateral(ML),and anterior-posterior(AP)directions(σSI,σML andσAP)in the femoral neck were 13.4 times,2.2 times and 1.9 times greater than those in the greater trochanter;the normal strains(εSI,εML,andεAP)in the femoral neck were 7.4 times,5.0 times,and 4.0 times greater than those of the greater trochanter regions.Conclusions Under the standing posture,the cortical and cancellous bone in the femoral neck was subjected to high stress and strain,indicating that the femoral neck was a region at high risk of fractures.This result was consistent with clinical observations.This study provided certain preliminary theoretical basis for the future application ofμMRI-FEA in clinical non-invasive assessment of fracture risk and identification of high-risk population.