腰椎单/双节段骨水泥强化椎弓根螺钉固定对邻近节段影响的有限元分析

Impact of cement-augmented pedicle screw instrumentation on adjacent segments degeneration in single or double-level lumbar spinal fusion: a finite element analysis

中文关键词:  腰椎内固定  椎弓根螺钉  骨水泥强化  邻近节段退变  有限元分析

英文关键词:Lumbar instrumentation  Pedicle screw  Cement-augmented  Adjacent segments degeneration  Finite element analysis

中文摘要:

  【摘要】 目的：比较腰椎后路单/双节段融合固定时普通椎弓根螺钉（pedicle screw，PS）固定和骨水泥强化椎弓根螺钉（cement-augmented pedicle screw，CAPS）固定对邻近节段退变（adjacent segments degeneration，ASD）的影响。方法：选取1例正常男性志愿者的腰骶部CT扫描数据，建立L3～S1的完整有限元模型。验证完整模型的有效性后，通过三维扫描仪扫描空心及实心椎弓根螺钉，构建较为仿真的三维螺钉模型，再分别建立L5～S1、L4～S1的PS固定和CAPS固定模型。在L3椎体上表面施加载400N的垂直向下载荷模拟人体自身重力，同时在L3椎体上表面于不同方向施加7.5N·m力矩，模拟脊柱前屈、后伸、左右侧弯和左右旋转等生理活动，比较模型间固定节段上位相邻近节段的椎间盘/小关节Von Mises应力极值和上位相邻节段活动度（ROM）的差异。结果：模型的有效性验证显示完整模型在各个方向上的ROM与已发表的尸体研究类似。在单节段固定时，PS固定的相邻椎间盘/小关节Von Mises应力极值和椎间ROM均略小于CPAS固定组。在双节段固定时，PS固定组相邻椎间盘/小关节Von Mises应力极值和ROM均小于CPAS固定组。两种固定方式中相邻节段椎间盘的应力分布规律基本类似，均分布在纤维环的外侧缘。结论：相比于PS固定，CAPS固定会增加相邻节段椎间盘/小关节的应力和椎间ROM，且在双节段固定时更为明显，可能会加速相邻节段的退变。

英文摘要:

  【Abstract】 Objectives: To compare the impact of pedicle screw(PS) fixation and cement-augmented pedicle screw(CAPS) fixation on adjacent segment degeneration(ASD) in single or double segment posterior lumbar fusion. Methods: An intact finite element model of L3-S1 segment was established by using CT scan data of a normal male volunteer. After verifying the validity of the intact model, the solid and fenestrated pedicle screws were scanned by a three-dimensional scanner to construct the screw models. Then, the PS fixation and CAPS fixation models were established respectively. A 400N vertical axial pre-load was imposed on the L3 superior surface and a 7.5N·m moment was also applied on the L3 superior surface to simulate 6 different physiological motions: flexion, extension, left bending, right bending, left rotation, and right rotation. The differencesof intervertebral disc/facet joint Von Mises stress and range of motion(ROM) on adjacent segments were compared between the models. Results: The validity study showed that the ROM of the intact model in all directions was similar to previous cadaveric studies. In single-level lumbar spinal fusion group, the intervertebral disc and facet joint Von Mises stress and ROM on adjacent segment were slightly lower in PS group than in CPAS group. In double-level lumbar spinal fusion group, the intervertebral disc and facet joint Von Mises stress and ROM on adjacent segment were lower in PS group than in CPAS group. The stress distributions of intervertebral disc on adjacent segments were similar in the two lumbar instrumentation groups, which were mainly on the edge of annulus fibrosus. Conclusions: The biomechanical analysis showed that, CAPS could increase ROM and stress of adjacent segment when compared with CPS, especially in double-level segments fusion, which might accelerate the adjacent segment degeneration.