TLIF术中最优化单侧螺钉植入和融合器放置的有限元分析

目的比较经单侧腰椎间孔椎体间融合(transforaminal lumbar interbody fusion,TLIF)中不同轴向植入角度椎弓根螺钉和不同放置位置融合器的生物力学特性。方法建立正常L3~5有限元模型,在验证其有效性基础上,在L4~5节段模拟后路双侧TLIF和4种不同组合类型椎弓根螺钉植入和融合器放置的单侧TLIF有限元重构模型,即:小角度植入椎弓根螺钉+对侧放置融合器(模型A)、小角度植入椎弓根螺钉+同侧放置融合器(模型B)、大角度植入椎弓根螺钉+同侧放置融合器(模型C)、大角度植入椎弓根螺钉+对侧放置融合器(模型D),分别比较4种重构模型在各种生理应力下的活动范围(range of the motion,ROM)以及螺钉、融合器与L4下终板界面的最大Von Mises应力差异。结果 4种单侧TLIF重构模型在融合节段(L4~5)ROM均较正常模型显著下降,但仍高于双侧TLIF重构模型。4种单侧TLIF重构模型稳定性比较,模型C下降最多,其在屈伸、侧屈和扭转应力下ROM分别减少约为正常模型的50.7%、89.9%和90.3%。螺钉和融合器与L4下终板界面最大Von Mises应力比较,相对于其他3组模型,模型C除了在同侧侧屈和扭转外的大部分应力下承受较小的应力。结论在单侧TLIF重构模型中选择大角度植入椎弓根螺钉和同侧放置融合器能够获得最佳的生物力学稳定性,通过缩小与双侧TLIF模型稳定性差异以减少断钉或融合器下沉的风险,值得临床推广运用。

Finite element analysis on the optimal unilateral pedicle screw-implanted angle and cage position for TLIF surgery

Objective To compare biomechanical properties of pedicle screw with different axial angles and interbody cage with different positions for unilateral transforaminal lumbar interbody fusion (TLIF) surgery. Methods The normal L3-5 finite element (FE) model was established and validated. Then one bilateral TILF reconstruction FE model and four unilateral TILF reconstruction FE models with different pedicle screw-cage combination types at L4-5 level were constructed, respectively. Namely, Model A (a small axial angle-implanted screw and an ipsilaterally-placed cage), Model B (a small axial angle-implanted screw and a contralaterally-placed cage), Model C (a large axial angle-implanted screw and an ipsilaterally-placed cage), Model D (a large axial angle-implanted screw and a contralaterally-placed cage). The range of motion (ROM) of 4 reconstruction models under various physiological stresses as well as the maximum Von Mises stresses on pedicle screw, cage-L4 inferior endplate were compared. Results The ROMs at fusion segment (L4-5) in 4 unilateral TLIF reconstruction models were significantly decreased compared with the normal model, but they were still larger than bilateral TLIF reconstruction model. For 4 unilateral TLIF reconstruction models, Model C showed the largest decrease in stability, and the ROM of Model C was 50.7%, 89.9%, 90.3% of the normal model in flexion-extension, lateral bending, axial rotation, respectively. When comparing the maximum Von Mises stress of posterior pedicle screw and cage-L4 inferior endplate in 4 unilateral TLIF reconstruction models, Model C could bear relatively smaller stress under most loading modes, except in ipsilateral lateral bending and axial rotation. Conclusions The unilateral TLIF reconstruction model with a large axial angle-implanted screw and an ipsilaterally placed-cage can achieve the optimal stability. By narrowing the difference in stability with the bilateral TILF model, the unilateral TLIF reconstruction model can reduce the risk of screw failure and cage subsidence, which is worth of clinical application.