中上胸椎皮质骨通道螺钉固定的生物力学有限元仿真研究

目的比较研究经皮质骨通道(cortical bone trajectory,CBT)螺钉系统和传统椎弓根螺钉系统在中上胸椎内固定中的生物力学性能。方法通过正常人T7～8节段CT扫描获取断层图像,利用Mimics软件重建人体T7～8三维模型,再通过FreeForm模型优化和ANSYS软件前处理功能建立中上胸椎有限元模型,并在此基础上分别建立椎间盘切除后CBT螺钉和椎弓根螺钉固定模型,对两组模型分别施加5 N·m前屈、后伸、侧弯和旋转载荷,比较分析椎体及植入物在不同工况下的位移及应力峰值。结果各载荷条件下,CBT螺钉组最大位移较椎弓根螺钉组偏低,CBT螺钉组活动度小于椎弓根螺钉组。两组模型的整体应力水平接近,CBT螺钉组偏低于椎弓根螺钉组。前屈、后伸及旋转载荷下,椎弓根螺钉组椎体的最大应力较CBT螺钉组分别降低31%、17%和18%;侧弯载荷下,CBT螺钉组椎体应力相对椎弓根螺钉组降低20%。前屈及旋转载荷下,椎弓根螺钉组椎体的最大应力小于CBT螺钉组,降低幅度分别为2%和11%;后伸及侧弯载荷下,CBT螺钉组椎体最大应力小于椎弓根螺钉组,降低幅度为11%和1%。结论 CBT螺钉在结构稳定性上优于传统椎弓根螺钉,整体应力分布上接近于椎弓根螺钉,但在椎体应力分布方面稍有逊色。研究结果为中上胸椎椎弓根螺钉固定失效后采用CBT螺钉固定的临床应用提供理论基础。

Biomechanical Evaluation of Upper-Middle Thoracic Vertebrae Fixed by Cortical Bone Trajectory Screws: A Finite Element Simulation Study

Objective To compare biomechanical properties of cortical bone trajectory (CBT) screw and traditional trajectory screw for fixing upper-middle thoracic spine. Methods The tomography images were obtained by CT scanning of normal T7 and T8 segments, and the three-dimensional (3D) model of T7-8 was reconstructed by Mimics software. The finite element model of upper-middle thoracic spine was established by optimizing FreeForm model and pre-processing function of ANSYS software. On this basis, the CBT screw and pedicle screw fixation models after discectomy were established, and 5 N·m flexion, extension, lateral bending and rotation loads were applied to the two model groups, respectively. The displacement and peak stress of vertebrae and implants under different working conditions were compared and analyzed. Results Under different loading conditions, the maximum displacement of CBT screw group was lower than that of pedicle screw group, and the range of motion of CBT screw group was lower than that of pedicle screw group. The stress level of both models was close, and the stress of CBT screw group was slightly lower than that of pedicle screw group. Under the load of flexion, extension and rotation, the maximum vertebral stress of pedicle screw group decreased by 31%, 17% and 18% compared with that of CBT screw group, and under lateral bending load, the vertebral stress of CBT screw group was 20% lower than that of pedicle screw group. Under the load of flexion and rotation, the maximum stress of pedicle screw group decreased by 2% and 11%; however, the maximum stress of CBT screw group was 11% and 1% lower than that of pedicle screw group. Conclusions The stability of CBT screw was better than that of pedicle screw, and the overall stress distribution was similar to that of pedicle screw. However, the vertebral stress distribution of CBT group was slightly inferior. The research findings provide a theoretical basis for the clinical application of cortical screw fixation after the failure in pedicle screw fixation for the upper-middle thoracic vertebrae.