腰椎行椎间孔入路椎间融合术固定的有限元分析

Finite element analysis on transforaminal lumbar interbody fusion treatment

目的 利用有限元方法分析经单侧椎间孔入路腰椎间融合术治疗腰椎退行性病变的临床可行性.方法 基于正常人L3～5节段的CT扫描数据,利用Mimics、Pro/E、ANSYS软件分别建立L3～5正常生理状态有限元模型、L4/5左单侧椎弓根螺钉内固定加椎间融合器模型（单侧TLIF）、L4/5双侧椎弓根螺钉内固定加椎间融合器模型（双侧TLIF）.在L3上表面施加500 N的人体重力和10N·m力矩,模拟人体直立、前屈、后伸、左侧弯和右旋5种生理活动,观察不同工况时椎体、椎间盘、螺钉及融合器上变形及应力分布情况,比较两种固定方法力学性能上的差异.结果 各种工况下单侧TLIF、双侧TLIF的L3～5节段变形量均较生理状态模型减少,单侧TLIF、双侧TLIF模型均在后伸运动时融合器的应力达到最大值,且单侧TLIF模型椎弓根螺钉上的应力峰值在各种工况中均明显高于双侧TLIF,后伸工况时应力峰值达到463.39 MPa.结论 单侧TLIF可作为腰椎退变性疾病的一种固定方法,但应力峰值均明显高于双侧TLIF模型,故系统稳定性差于双侧TLIF模型,提示患者在康复过程中应减少后伸运动,以免发生手术失效或螺钉断裂.

Objective To analyze the clinical feasibility of unilateral transforaminal lumbar interbody fusion （TLIF） for treating lumbar degenerative diseases by finite element method.Methods Based on CT scan data,three-dimensional （3D） finite element models of the normal L3-5 segments under physiological status （intact lumbar model）,L4/5 with unilateral pedicle screw fixation plus interbody fusion （unilateral TLIF model） and L4/5 with bilateral pedicle screw fixation plus interbody fusion （bilateral TLIF model） were established by using Mimics,Pro/E,ANSYS software,respectively.Preload of 500 N and load of 10 N · m torque were applied on the superior surface of the L3 segment to simulate 5 physiological activities：body upright,flexion,extension,left lateral bending and right axial rotation.The deformation and stress distributions in vertebral body,vertebral discs,pedicle screw and cage under different loads were then recorded and analyzed to compare mechanical properties of the two fixation methods.Results The deformation of L3-5 segments fixed with unilateral TLIF or bilateral TLIF decreased as compared to the intact lumbar model; the stresses in cage reached the maximum in both unilateral TLIF model and bilateral TLIF model during back extension,meanwhile peak stresses on pedicle screws in unilateral TLIF were significantly higher than those on bilateral TILF model,with the peak stress of 463.39 MPa during back extension.Conclusions Unilateral TLIF can be selected as a method for treating lumbar degenerative diseases; however,its stability was inferior to bilateral TLIF due to the higher peak stress.Therefore,less stretch exercises may be safe for patients during rehabilitation to avoid surgery failure or pedicle screw fracture.