【摘要】 背景:与基于面骨密度的临床工具相比,特定载荷条件下的有限元模型强度分析越来越多用于改善对骨折风险的评估。然而,大多数有限元模型仅限于估计骨强度和可能发生骨折的位置,不能对骨折过程本身进行建模。目的:在ABAQUS软件中使用扩展有限元法对股骨颈骨折裂纹进行模拟,采用基于最大主应力和能量的准则来确定裂纹的起裂位置和裂纹扩展路径。方法:收集1名健康志愿者股骨近端CT数据,以DICOM格式导入Mimics重建三维模型,赋予皮质骨、松质骨相应材料参数。最初进行静态分析,以评估骨应力分布并确定骨折危险区域。基于应力结果和排除边界附近的单元,定义了允许在扩展有限元法分析中发生断裂的富集区,当主应力超过116 MPa时单元发生裂纹萌生,预测裂纹位置与演变过程。结果与结论:(1)静力学分析:在站立位载荷下,股骨颈出现应力集中,最大等效应力为711.8 MPa,根据第四强度理论,股骨皮质骨屈服强度为116 MPa,当前载荷下股骨颈将发生不可逆的塑性破坏。此外,最大主应力集中于股骨颈外侧,最大值超过116 MPa。(2)裂纹扩展分析:裂纹的产生是一个蓄积能量的过程,随着应力不断增大并超过阈值时,股骨颈外上方开始出现单元损伤,此时为黏性裂纹状态,仍有抗断能力。随着应力继续增大,该单元完全失效,此时裂纹面周围及尖端应力值迅速降低,应力集中向单元两侧分布。裂纹先后向股骨颈前上、后下方向延伸,最终形成股骨颈骨折。(3)基于断裂力学建立的股骨近端骨折模型,既能很好地预测弹性行为,又能很好地预测站立载荷下的断裂裂纹路径及评估力学性能和临界主应力的影响,同时强调了充分校准断裂标准的重要性。该方法较强度理论建模方法提供了更多关于骨折裂纹扩展机制的信息,有助于对骨折潜在风险的深入探究。更多还原

【Abstract】 BACKGROUND: Compared with clinical tools based on facial bone mineral density, finite element model strength analysis under specific load conditions is more and more used to improve fracture risk assessment. However, most finite element models are limited to the estimation of bone strength and the location of possible fractures, but cannot model the fracture process itself. OBJECTIVE: The crack of femoral neck fracture was simulated by extended finite element method in ABAQUS, and the crack initiation position and crack propagation path were determined based on the criterion of maximum principal stress and fracture energy.METHODS: The CT data of the proximal femur of a healthy volunteer were collected and imported into Mimics to reconstruct the three-dimensional model in DICOM format. The corresponding material parameters of osteoporotic cortical bone and cancellous bone were given. Static analysis was initially performed to assess bone stress distribution and identify fracture risk areas. Based on the stress results and excluding the elements near the boundary, the enrichment area which allowed fracture to occur in extended finite element method analysis was defined. When the principal stress exceeded 116 MPa, the crack initiation occurred in the element, which could predict crack location and evolution process. RESULTS AND CONCLUSION:（1） Static analysis: Under the standing load, the stress concentration appeared in the femoral neck, and the maximum equivalent stress was 711.8 MPa. According to the fourth strength theory, the yield strength of the cortical bone of the femur was 116 MPA, and irreversible plastic failure would occur in the femoral neck under the current load. In addition, the maximum principal stress was concentrated on the lateral side of the femoral neck, and the maximum value was higher than that of 116 MPa.（2） Crack propagation analysis: The generation of crack was a process of accumulating energy. When the stress increased and exceeded the threshold, the unit damage began to appear at the upper and outer part of the femoral neck. At this time, it was in the state of viscous crack and still had the ability to resist fracture. As the stress continued to increase, the element failed completely. At this time, the stress around the crack surface and the tip decreased rapidly, and the stress concentration was distributed to both sides of the element. The crack extended to the anterior superior and posterior inferior direction of the femoral neck, and finally formed the fracture of the femoral neck.（3） The proximal femoral fracture model based on fracture mechanics could predict not only the elastic behavior, but also the fracture crack path under standing load. It emphasized the importance of fully calibrating fracture criteria and evaluated the effects of mechanical properties and critical principal stress. Compared with the modeling method of strength theory, this method provides more information about the mechanism of fracture crack propagation and is helpful to explore the potential risk of fracture.更多还原