骨质疏松腰椎椎弓根螺钉轴向抗拔出力的有限元分析

Finite element analysis of axial pull-out strength in osteoporotic lumbar pedicle screws

中文关键词:  骨质疏松  椎弓根螺钉  皮质骨轨迹螺钉  有限元分析  生物力学  抗拉强度

英文关键词:Osteoporosis  Pedicle screw  Cortical bone trajectory  Finite element analysis  Biomechanics  Tensile strength

中文摘要:

  【摘要】 目的：通过有限元分析比较6种螺钉强化技术在骨质疏松腰椎后路椎弓根内固定的生物力学结果，为内固定螺钉的优化和选择提供参考。方法：选取7例无腰椎病变及手术史的男性腰椎CT数据，年龄68.0±4.9（60~75）岁，身高171.7±3.2（168~176）cm，体重63.6±3.2（59~68）kg，采用64排螺旋CT进行连续薄层扫描，获取DICOM格式影像。通过Mimics 21.0软件重建L3椎体三维模型，经Geomagic Wrap 2021完成曲面优化后，在SolidWorks 2023中构建7种螺钉模型并进行装配。按强化方式将螺钉分为：A组（对照组，传统螺钉无加固）、B组（增大螺钉外径）、C组（减小螺距）、D组（减小皮质骨接触部分的螺距）、E组（骨水泥加固）、F组（穿透对侧皮质骨）、G组（皮质骨轨迹螺钉）。建立7种螺钉×7例椎体模型的49组有限元模型，参考既往研究文献数据完成材料赋值后，采用Ansys Workbench 2023静态结构分析模块，对所建立的7组有限元模型模拟轴向拔出实验，观察各组螺钉在1200N的轴向拉力下的拔出位移及破坏时产生的最大等效应力，并对所测指标进行不同螺钉组之间的对比分析。组间对比采用单因素方差分析，实验组分别与对照组对比分析采用独立样本t检验。结果：A~G组螺钉的最大位移分别为：0.142±0.029mm、0.138±0.031mm、0.144±0.032mm、0.139±0.027mm、0.119±0.024mm、0.126±0.028mm、0.040±0.007mm，A~F组间比较差异无统计学意义（F=0.812，P=0.5489）。A组与G组对比差异有统计学意义（P<0.001）；最大等效应力分别为264.0±7.6MPa、234.8±28.0MPa、245.5±17.5MPa、260.0±7.2MPa、279.7±14.3MPa、311.9±31.4MPa、432.6±87.5MPa。B组、C组与A组对比分别减小了11.1%、7%，差异有统计学意义（P<0.05），D组与A组对比差异无统计学意义（P>0.05），E~G组分别与A组对比分别增大了5.9%，18.1%，63.9%，差异有统计学意义（P<0.05）。结论：不同螺丝钉强化技术抗轴向拔出力效果明显不同，仅增大螺钉外径或减小全部螺距会减小螺钉的轴向拔出强度，减小皮质骨区域的螺距对螺钉把持力的增加没有明显正向作用，骨水泥加固、增加螺钉长度穿透对侧皮质骨和皮质骨轨迹螺钉均明显改善了螺钉的轴向抗拔出效果，其中皮质骨轨迹螺钉强化技术的加固效果最为显著。

英文摘要:

  【Abstract】 Objectives: To compare the biomechanical outcomes of six different screw reinforcement methods for posterior lumbar pedicle screw augmentation technique in osteoporotic vertebrae through finite element analysis, and provide a reference for the optimization and selection of internal fixation screws. Method: The lumbar CT scan data from seven males without lumbar pathologies or surgical history were obtained. Age: 68.0±4.9 years(60-75), height: 171.7±3.2cm (168-176), weight: 63.6±3.2kg(59-68). Continuous thin-layer scanning was performed using a 64-slice spiral CT to obtain DICOM images. The L3 vertebral 3D models were reconstructed using Mimics 21.0 software, after optimizing for surface geometry in Geomagic Wrap 2021, seven models of screw were designed and assembled in SolidWorks 2023. Screws were categorized into seven groups based on reinforcement methods: Group A(Control group, no reinforcement), Group B(increasing thread outer diameter), Group C(decreasing pitch), Group D(decreasing the part of pitch contacted cortical bone), Group E(bone cement reinforcement), Group F(penetrating the opposite cortex), and Group G(cortical bone trajectory screws). 49 finite element models(7 screw types × 7 vertebrae) were established. After material property assignments based on the data from prior research literature, the Static Structural Analysis module of Ansys Workbench 2023 was employed to simulate axial pull-out experiments on the seven established finite element models. The pull-out displacement under an axial tension of 1,200N and the maximum equivalent stress when the screw was damaged were analyzed. Intergroup comparisons employed one-way ANOVA, with independent-sample t-tests for experimental vs. control group comparisons. Results: The maximum displacements of Groups A-G were 0.142±0.029mm, 0.138±0.031mm, 0.144±0.032mm, 0.139±0.027mm, 0.119±0.024mm, 0.126±0.028mm, 0.040±0.007mm, respectively. No statistically significant differences were observed between Groups A to F(F=0.812, P=0.5489). Group G demonstrated a statistically significant difference compared to Group A(P<0.001). The maximum equivalent stress of groups A-G were 264.0±7.6MPa, 234.8±28.0MPa, 245.5±17.5MPa, 260.0±7.2MPa, 279.7±14.3MPa, 311.9±31.4MPa, 432.6±87.5MPa. Compared with group A, group B decreased by 11.1%, and group C decreased by 7%, and the differences were statistically significan(P<0.05); Group D wasn′t significantly different from group A(P>0.05); Compared with group A, groups E-G increased by 5.9%, 18.1% and 63.9%, respectively, and the differences were statistically significant(P<0.05). Conclusions: Different screw augmentation techniques demonstrated significantly different effects on axial pull-out strength. Increasing the outer diameter of the screw or decreasing the total pitch will reduce the axial pull-out strength of the screw, and reducing the pitch in the cortical bone area has no obvious positive effect on increasing the holding force of screw. Bone cement reinforcement, increasing the screw length in penetrating contralateral cortical bone, and cortical bone trajectory screw can all significantly improve the axial anti-pullout effect of the screw, among which Cortical bone trajectory screw augmentation technique has the most significant effect.