斜外侧椎间融合术融合器沉降对腰椎生物力学影响的有限元分析

Finite element analysis of lumbar biomechanical effects of cage subsidence in oblique lateral interbody fusion

目的:应用三维有限元法分析椎间融合器(cage)沉降对斜外侧椎间融合术(oblique lateral interbody fusion,OLIF)术后腰椎生物力学的影响。方法:根据1例健康成年人腰椎CT扫描数据构建正常腰椎L3~L5节段三维有限元模型,模拟进行L4/5节段OLIF手术,根据cage沉降陷入椎体程度(0、1%~25%、26%~50%、51%~75%、76%~100%)分为5个等级(Grade0、Grade1、Grade2、Grade3、Grade4),共构建10组模型(单纯cage沉降组5组、附加后路双侧椎弓根钉棒固定的钉棒组5组)。固定L5椎体下表面,设定400N的预加载荷于L3椎体上表面,再施加10N·m的力矩来模拟脊柱的前屈、后伸、侧屈、旋转运动。对腰椎在不同生理运动下L4/5节段活动度(range of motion,ROM)、cage应力峰值和内固定钉棒应力峰值进行分析。结果:模型在不同生理运动下L3/4和L4/5椎体的ROM与已发表的尸体研究类似,证明了模型的有效性。对模型施加载荷的6种运动状态中,沉降组Grade3的ROM最大,cage最大应力峰值发生在Grade2前屈运动时,达到了82.7Mpa,相较Grade0增加了241%。在附加椎弓根钉棒后脊柱ROM及cage应力峰值均减小,尤以Grade2变化最为显著,与未附加内固定相比,Grade2平均ROM下降了63%,后伸运动下cage应力峰值减小51%。结论:cage沉降对腰椎生物力学影响较大,其中cage沉降51%~75%时脊柱稳定性最差,cage沉降26%~50%时cage进一步塌陷风险最高,附加内固定钉棒后可增加脊柱稳定性并降低沉降风险。

Objectives:To analyze the effect of cage subsidence on the biomechanics of the lumbar spine after oblique lateral interbody fusion(OLIF)using three-dimensional finite element method.Methods:To construct a three-dimensional finite element model of the L3-L5 segments of the normal lumbar spine according to the CT scan data of a case of a healthy adult,to simulate the L4/5 segment OLIF surgery,and to construct Grade0,Grade1,Grade2,Grade3 and Grade4 according to the degree of cage subsidence into the vertebral body 0,1%-25%,26%-50%,51%-75%and 76%-100%of the vertebral body.Constructed a total of10 groups of models(5 groups of stand-alone subsidence and 5 groups of additional posterior bilateral pedicle screws).The lower surface of the L5 vertebral body was fixed,a preloaded load of 400 N was set on the upper surface of the L3 vertebral body,and a torque of 10 N·m was applied to simulate the anterior flexion,posterior extension,lateral flexion,and rotational motion of the spine.The L4/5 range of motion(ROM),peak cage stresses and peak stresses of the pedicle screw fixation system were analysed for different physiological movements of the lumbar spine.Results:The ROM of the model for L3/4 and L4/5 vertebrae under different physiological motions was similar to published cadaver studies,demonstrated the validity of the model.Of the six states of motion to which the model was loaded,the ROM of Grade3 in the sedimentation group was the largest,and the maximum stress of cage occurred in the forward flexion movement of Grade2,which reached82.7 MPa,an increase of 241%compared with Grade0.After the addition of pedicle screw fixation system,the peak stress of ROM and cage in the spine decreased,especially the change of Grade2 was the most significant.Compared with stand-alone cage subsidence,the average ROM of Grade2 decreased by 63%,and the peak stress of cage decreased by 51%under the extension exercise.Conclusions:Cage subsidence has a great influence on the biomechanics of the lumbar spine,in which the stability of the spine is the worst when the cage subsidence is 51%-75%,and the risk of further collapse of the cage is the highest when the cage subsidence is 26%-50%.The addition of pedicle screw fixation system can increase the stability of the spine and reduce the risk of subsidence.