椎间融合与双侧经椎弓根经椎间盘螺钉置入后腰椎生物力学的有限元分析

Finite element analysis of lumbar vertebra biomechanics after transforaminal lumbar interbody fusion combined with bilateral transpedicular transdiscal lumbar screw fixation

背景:腰椎经椎弓根经椎间盘螺钉是一种新的微创脊柱内固定技术,与传统双侧椎弓根螺钉固定相比,单侧只需1枚螺钉固定1个节段,具有经济微创、操作便捷等优点。但目前探讨应用双侧经椎弓根经椎间盘螺钉联合改良经椎间孔入路腰椎椎间融合(transforaminal lumbar interbodyfusion,TLIF)术式的研究仍很少见。目的:通过建立改良TLIF无内固定(cage alone)、改良TLIF联合双侧椎弓根螺钉内固定(cage+BPS)和改良TLIF联合双侧经椎弓根经椎间盘螺钉内固定(cage+BTPTDS)3种有限元模型,评估改良TILF联合不同内固定对椎间融合器(cage)、内固定、椎间盘、下终板的应力分布及腰椎活动度的影响。方法:采集成人腰椎薄层CT扫描图像,通过Mimics、Geomagic和SolidWorks软件建立3种有限元模型:cage alone模型、cage+BPS模型和cage+BTPTDS模型。采用ANSYS Workbench模拟施加人体前屈、后伸、左侧弯、右侧弯、左侧旋转、右侧旋转6种不同运动载荷,计算3种模型cage及内固定、下终板、椎间盘应力分布和腰椎活动度的差异,比较3种不同手术方案对腰椎生物力学效应的影响。结果与结论:①成功构建了3种有限元模型:cage alone、cage+BPS和cage+BTPTDS;②cage+BTPTDS模型在前屈、侧弯运动载荷下,其cage最大应力小于cage alone模型,稍大于cage+BPS模型;在后伸运动载荷下,cage+BPS模型的cage最大应力明显小于其余两种模型;在旋转载荷下,cage+BTPTDS模型与cage+BPS模型cage最大应力接近,小于cage alone模型;③在屈伸载荷下,cage+BTPTDS模型内固定最大应力明显大于cage+BPS模型;在侧弯载荷下,cage+BTPTDS模型与cage+BPS模型二者内固定最大应力接近;而在旋转载荷下,cage+BTPTDS模型内固定最大应力则小于cage+BPS模型;④cage+BPS模型的融合节段下终板最大应力介于另外两者之间;⑤cage+BTPTDS模型在前屈、后伸、侧弯、旋转工况下,其活动度与cage alone模型差异不大;⑥结果表明,改良TLIF联合双侧经椎弓根经椎间盘螺钉内固定既能够带来良好的稳定性,又能够保证腰椎整体活动度,具有良好的生物力学效应。

BACKGROUND:Transpedicular transdiscal lumbar screw is a new type of spinal minimally invasive internal fixation technology.Compared with traditional bilateral pedicle screws,only one screw is needed to fix one segment on one side.It has the characteristics of being more economical,less trauma and easy to operate.However,studies on the application of transpedicular transdiscal lumbar screws combined with transforaminal lumbar interbody fusion(TLIF)and fixation are still rare.OBJECTIVE:To evaluate the effect of TLIF combined with various surgery methods on stress distribution of cage,fixation,disc lower and endplate and range of motion of lumbar vertebrae by constructing three kinds of finite element models including modified TLIF(cage alone)model,modified TLIF combined with bilateral pedicle screw(cage+BPS)model and modified TLIF combined with bilateral transpedicular transdiscal lumbar screw(cage+BTPTDS)model.METHODS:The CT images of the adult lumbar spine were used to establish the three kinds of TLIF finite element models:cage alone,cage+BPS and cage+BTPTDS using software Mimics,Geomagic and SolidWorks.ANSYS Workbench was used to simulate the application of six different motion loads of human body flexion and extension,left and right bending,and left and right rotation to calculate stress distribution and the changes in the range of motion of the lumbar spine of the cage,fixation,endplate and disc of the three lumbar spine surgery models and to compare the effects of three surgical options on the biomechanical effects of the lumbar spine.RESULTS AND CONCLUSION:(1)The cage alone model,cage+BPS model and cage+BTPTDS model were constructed successfully.(2)In flexion and lateral bending conditions,the maximum stress of the cage of cage+BTPTDS model was smaller than that of the cage alone model and a little greater than that of the cage+BPS model.In the extension condition,the maximum stress of the cage of the cage+BPS model was obviously smaller than that of the other two models.When it came to rotating condition,the maximum stress of the cage in the cage+BPS model and the cage+BTPTDS model presented no obvious difference,which was both smaller than the cage alone model.(3)The maximum stress of fixation of the cage+BTPTDS model was obviously bigger than the cage+BPS model in flexion and extension conditions,close to the cage+BPS model in lateral bending conditions,and smaller than the cage+BPS model in rotation conditions.(4)The maximum stress of the lower endplate of the fusion segment of the cage+BPS model was between the two other models.(5)In terms of the range of motion,the cage+BTPTDS model presented no obvious difference with that of the cage+BPS model at flexion and extension,left and right bending,and left and right rotation.(6)It is concluded that modified TLIF combined with transpedicular transdiscal lumbar screw provides stable support for the vertebral body of the fusion segment,ensures the motion range of the lumbar spine and has a good biomechanical effect.