股骨头坏死中松质骨微观力学特性的演变规律

目的采用结合显微CT和显微有限元分析方法,即基于显微CT图像建立三维有限元模型并进行数值模拟仿真分析,无创研究不同分期的坏死股骨头松质骨的微结构和微观力学性能,以期了解在股骨头坏死的发展过程中,松质骨微结构和微观力学特性的变化规律,为临床预测股骨头坏死提供理论基础。方法采集10例股骨头坏死患者的股骨头标本的显微CT图像,按照国际骨循环研究学会分期标准分为Ⅱ期样本3例,Ⅲ期3例,Ⅳ期4例。将图像中骨组织进行阈值分割,分区域建立坏死区、侧向区、硬化区和远端区的松质骨块三维有限元模型(边长8 mm),并根据CT值赋予非均匀材料属性。利用ImageJ软件中的BoneJ插件通过识别显微CT组图像,计算测量各区域松质骨的微结构参数,包括骨体积分数、骨小梁厚度、骨小梁间隙、结构模型指数。对松质骨块施加表观应变为1%的压缩载荷,计算骨组织应力和松质骨表观刚度等参数,对比分析各分期、各分区结果。结果在松质骨微结构方面,Ⅳ期较Ⅱ期的股骨头内部硬化区和坏死区的变化最为明显,硬化区的骨体积分数不断上升,骨小梁间隙下降,结构模型指数减小,而坏死区域与之相反;在骨组织微观受力方面,Ⅱ期到Ⅲ期坏死区域的应力并没有明显变化,而硬化区域随着分期增加应力不断上升,侧向区的应力不断下降。表观刚度变化与应力变化一致。结论随着股骨头坏死程度的加剧,硬化区的松质骨微结构和力学性能变化最大,应作为临床早期诊断中重点关注的区域。此外,微结构参数并不能准确体现松质骨的力学行为,而股骨头塌陷最终取决于其力学特性,因此结合有限元分析方法可更加全面了解股骨头坏死的微观力学演变规律。

Evolution of micromechanical properties of cancellous bone in osteonecrosis of the femoral head

Objective In this study,the microstructure parameters and mechanical properties of the trabecular bone in different areas of the femoral head in different periods were compared by combining the methods of micro CT and finite element analysis,which meant 3D finite element model based on micro CT image and numerical simulation analysis,to understand the changes of the internal trabecular bone in the pathogenesis of the osteonecrosis of the femoral head and provide a theoretical basis for clinical prediction of the necrosis of the femoral head.Methods Ten cases of osteonecrosis of the femoral head were scanned by micro CT.Among them,there were 3 cases in the second stage,3 cases in the third stage and 4 cases in the fourth stage according to the ARCO stage.The three-dimensional finite element models of trabecular bone cube of necrotic area,lateral area,sclerotic area and distal area(side length 8 mm)were established in different regions,and the heterogeneous material attribute was given according to the CT value.ImageJ software was used to identify the images of the micro CT,and the microstructure parameters of the trabecular bones in each region were calculated,including bone volume fraction,bone trabecular thickness,bone trabecular space and structural model index.The trabecular bones were tested under the compression load of 1%of the apparent strain.The stress of bone tissue and the apparent stiffness of cancellous bone were calculated,and the results of different stages and zones were compared.Results In the aspect of microstructure,the sclerotic area and necrotic area of the femoral head changed the most from stageⅡto stage Ⅳ,the bone volume fraction of the sclerotic area increased continuously,the trabecular separation decreased,the structure model index decreased,and the necrotic area was the opposite.In the aspect of microstructure stress of bone,the stress of necrotic area in stageⅡto stageⅢdid not change obviously,while the stress in sclerotic area increased with the increase of stages.The stress in the lateral region decreased.The change of apparent stiffness is consistent with the change of stress.Conclusions With the aggravation of the necrosis of the femoral head,the microstructure and mechanical properties of the cancellous bone in the sclerotic area change the most,which should be the focus of early clinical diagnosis.In addition,the microstructure parameters can not accurately reflect the mechanical behavior of trabecular bone,and the collapse of the femoral head ultimately depends on its mechanical properties.Therefore,combining with the finite element analysis method,we can more comprehensively understand the micromechanical evolution law of femoral head necrosis.