斜外侧椎间融合联合单侧椎弓根钉棒固定术的三维有限元分析

Three-dimensional finite element analysis of oblique lateral lumbar interbody fusion combined with unilateral pedicle screw fixation

目的:运用三维有限元分析法验证斜外侧椎间融合术(oblique lateral interbody fusion,OLIF)辅助单侧椎弓根钉棒固定能否为相应单一融合固定节段提供足够的椎间稳定性。方法:在健康人L3~S1节段CT扫描数据的基础上,利用Mimics、Geomagic、3-Matic软件建立L3~S1三维有限元模型,设定为正常对照组(M0),以此为基础联合使用Freeform等软件分别建立L4/5节段OLIF单纯融合固定(Stand alone)模型(M1)、OLIF辅助单侧椎弓根钉棒固定(Wiltse入路)模型(M2)、OLIF辅助双侧椎弓根钉棒固定(Wiltse入路)模型(M3)。设定500N预载荷作用于L3顶端,再施加10N·m的力矩模拟脊椎直立、前屈、后伸、侧屈及旋转等生理活动,按上述加载条件作用于M0,对模型有效性性进行验证,同时按相同加载条件作用于各有限元模型,观察各有限元模型不同工况下L4/5节段相对活动度(ROM)、椎间融合器和椎弓根钉棒应力分布状况,记录最大应力值。结果:通过与文献数据比较,本有限元模型L4/5节段ROM在不同运动状态下与前人研究结果相近,证明本模型具备有效性。4组有限元模型前屈、后伸、左右侧弯、左右旋转运动状态下ROM值由小到大排序为M3、M2、M1、M0。M2相比M0、M1能较好地控制前屈和后伸,M2的ROM相比M0前屈后伸时变化幅度分别为75.43%、85.20%,相比M1变化幅度分别为58.88%、70.39%。M3相比M2前屈和后伸时稳定性亦较好,M3的ROM相比M2前屈后伸时变化幅度分别为25.55%、25.33%。除外变化幅度差异较小的右侧弯和右旋转状态,M2较M0的ROM变化幅度远大于M2与M3之间ROM的变化幅度。M2相较M0各工况下ROM变化幅度为14.08%~85.20%,M2相较M3各工况下ROM变化幅度为16.44%~25.55%。椎间融合器应力值方面,除直立时M2应力峰值略高于M1,其余运动状态下OLIF各手术组融合器应力峰值随着附加椎弓根钉棒数量的增加而表现出一定的下降趋势,这种趋势以后伸时表现最明显,幅度变化为109.14%。钉棒应力峰值方面,M2钉棒应力峰值除右侧弯时明显低于M3,左侧弯时略低于M3,其余运动状态下其钉棒应力峰值均高于M3,二者应力差异以右侧弯和后伸时较大,M2较M3分别变化-33.09%和76.79%。三组模型钉棒及椎间融合器应力峰值均远未达到其屈服强度。结论:OLIF联合单侧椎弓根钉棒固定模型可以为相应融合固定节段提供足够的椎间稳定性。

Objectives: To validate whether oblique lateral interbody fusion(OLIF) combined with unilateral pedicle screw -rod fixation can provide sufficient interbody stability for corresponding fusion and fixation segment through three-dimensional finite element analysis. Methods: To establish a three-dimensional finite element model of L3-S1 segments by Mimics, Geomagic, and 3-Matic software based on CT scan data of L3-S1 of healthy people, and it was set as normal control group(M0). On such basis, combined with Freeform and other software, OLIF stand alone model (M1) of L4/5, OLIF with unilateral pedicle screw-rod fixation (Wiltse approach) model(M2), and OLIF with bilateral pedicle screw-rod fixation(Wiltse approach) model(M3) were set up. 500N preload was applied on the upper surface of L3 and 10N·m moment was applied to simulate the physiological activities of lumbar spine in standing position, flexion, extension, lateral flexion and rotation. The above loading conditions were applied on both the M0, to validate the effectiveness of the model, and all finite element models, to observe the L4/5 segment range of motion(ROM), stress distribution of cage and pedicle screw -rod under different working conditions. The maximum stress of cage and pedicle screw-rod should be recorded. Results: It was validated that the finite element model was effective compared with the literature data. The ROM values of 4 groups in each movement state(flexion, extension, left and right lateral flexion, left and right rotation) were ranked from small to large: M3, M2, M1, and M0. M2 showed better stability in flexion and extension than M0 and M1. To be specific, the variation ranges under flexion and extension condition of M2 ROM were 75.43% and 85.20% respectively comparing to M0, and 58.88% and 70.39% respectively comparing to M1. M3 showed better stability in flexion and extension than M2, and the variation ranges of M3 ROM were 25.55% and 25.33% under flexion and extension respectively comparing to M2. Except smaller difference of variation range under right bending and right rotation conditions, the variation range of ROM of M2 comparing with M0 was much larger than that comparing with M3. Under all working conditions, the variation ranges of ROM of M2 when compared with M0 were 14.08%-85.20%, and that were 16.44%-25.55% when compared with M3. In terms of the peak stress of the cage, except that it was slightly higher in M2 than in M1 under condition of standing, in other motion states, it showed a decreasing trend with the increase of the number of additional pedicle screw-rod, which was most obvious in extension with a decreasing range of 109.14%. In terms of the peak stress of the screw -rod system, it was higher in M2 than in M3 under other states, except that peak stress value of M2 significantly lower than that of M3 in right lateral flexion and slightly lower than that of the M3 in left lateral bending. The differences of peak stress of screw-rod system between M2 and M3 were larger in right lateral bending and retroextension which were -33.09% and 76.79%. The peak stress of the screw-rod and cage in each of the three surgery groups was far from their yield strength respectively. Conclusions: The model of OLIF with unilateral pedicle screw-rod fixation can provide sufficient intervertebral stability for the corresponding fusion fixation segment.