Biomechanical effects of posterior lumbar interbody fusion with vertical placement of pedicle screws compared to traditional placement

BACKGROUND The pedicle screw technique is widely employed for vertebral body fixation in the treatment of spinal disorders.However,traditional screw placement methods require the dissection of paraspinal muscles and the insertion of pedicle screws at specific transverse section angles(TSA).Larger TSA angles require more force to pull the muscle tissue,which can increase the risk of surgical trauma and ischemic injury to the lumbar muscles.AIM To study the feasibility of zero-degree TSA vertical pedicle screw technique in the lumbosacral segment.METHODS Finite element models of vertebral bodies and pedicle screw-rod systems were established for the L4-S1 spinal segments.A standard axial load of 500 N and a rotational torque of 10 N/m were applied.Simulated screw pull-out experiment was conducted to observe pedicle screw resistance to pull-out,maximum stress,load-displacement ratio,maximum stress in vertebral bodies,load-displacement ratio in vertebral bodies,and the stress distribution in pedicle screws and vertebral bodies.Differences between the 0-degree and 17-degree TSA were compared.RESULTS At 0-degree TSA,the screw pull-out force decreased by 11.35%compared to that at 17-degree TSA(P<0.05).At 0-degree and 17-degree TSA,the stress range in the screw-rod system was 335.1-657.5 MPa and 242.8-648.5 MPa,separately,which were below the fracture threshold for the screw-rod system(924 MPa).At 0-degree and 17-degree TSA,the stress range in the vertebral bodies was 68.45-78.91 MPa and 39.08-72.73 MPa,separately,which were below the typical bone yield stress range for vertebral bodies(110-125 MPa).At 0-degree TSA,the load-displacement ratio for the vertebral bodies and pedicle screws was slightly lower compared to that at 17-degree TSA,indicating slightly lower stability(P<0.05).CONCLUSION The safety and stability of 0-degree TSA are slightly lower,but the risks of screw-rod system fracture,vertebral body fracture,and rupture are within acceptable limits.

腰椎椎弓根通道不同外偏角方向变化规律的数字解剖学研究

目的：探讨腰椎椎弓根在0°头尾偏角和不同外偏角方向通道的变化规律。方法：1例健康成人腰椎CT连续扫描数据集，应用Mimics8．11三维重建腰椎数字解剖模型，将腰椎数字模型导人Surface10．0，确定椎骨正中矢状切面和经椎弓根中部水平面为0°正交平面，0°水平面为0°头尾偏角参考平面，正中矢状切面为0°内外偏角参考平面，确定左右椎弓根各个方向通道的正投影，获得椎弓根通道的正投影内边界及内边界内、外切圆，获得内切圆在正投影方向经椎板、椎弓根与椎体的通道长度及各内、外切圆圆心坐标值、半径大小，对获取相关数据进行定量分析与可视化显示。结果：L1-5左右椎弓根通道在0°头尾偏角和不同外偏角方向正投影区内边界的内切圆半径随外偏角的增大逐渐增大而后又逐渐减小，其中最大半径值对应的角度方向为最佳角度方向，外切圆半径没有明显变化；L1-5左右椎弓根通道正投影区内边界内切圆通道长度随外偏角的增大呈逐渐增大趋势。结论：腰椎椎弓根通道大小是随外偏角方向不同而不同的连续的动态变化过程，应用数字技术可以获得其通道大小连续的动态的变化规律，临床应用选择合适直径、长度大小的螺钉及确定最佳进钉方向需要依循这一规律。

影像定位结合椎弓根漏斗技术置入椎弓根螺钉的效果分析

目的:探讨影像定位结合椎弓根漏斗技术置入椎弓根螺钉(Pedicle screw,PS)的方法。方法:2005年6月～2006年12月以棘突为定位标志,寻找X片上椎弓根投影坐标,术中切除该投影区椎板外侧皮质,并挖除部分松质骨,直视下置入椎弓根螺钉506枚(121例),术后行CT扫描并记录椎弓根螺钉螺纹对椎弓根皮质的侵犯分度、椎弓根轴线与椎弓根螺钉轴线的水平位夹角(transverse section angle,TSa)、X线侧位片上椎弓根螺钉轴线与椎体上终板平行线的矢状位成角(sagital section angle,SSa)及椎弓根螺钉与椎体前缘的距离,以衡量椎弓根螺钉置入的效果。结果:506枚椎弓根螺钉均一次性成功置入,499枚对椎弓根形成Ⅰ度侵犯,7枚为0度侵犯,无螺钉破入椎管内,测量椎弓根螺钉TSa角度平均为(-0.41±1.07)°,SSa角度平均为(-0.39±0.67)°,PS与椎体前缘距离平均为(0.31±0.59)mm。结论:影像定位结合椎弓根漏斗技术是一种能够准确置入适当长度及直径的椎弓根螺钉,从而提供牢固的椎弓根螺钉稳定性,为临床提供了又一种准确置入椎弓根螺钉的方法。