变径螺钉与传统椎弓根螺钉在不同骨质疏松分级L4椎体的生物力学性能对比有限元分析

Comparison of the biomechanical properties between variable diameter screws and conventional pedicle screws in L4 vertebrae with different osteoporosis grading-finite element analysis

中文关键词:  有限元分析  骨质疏松分级  变径全皮质骨螺纹螺钉  改良皮质骨轨迹  生物力学

英文关键词:Finite element analysis  Osteoporosis grading  Variable diameter all-cortical bone threaded screws  Modified cortical bone trajectory  Biomechanics

中文摘要:

  【摘要】 目的：采用有限元分析方法，评估传统椎弓根轨迹置钉（traditional trajectory，TT）技术与改良皮质骨轨迹置钉（modified cortical bone trajectory，MCBT）技术在不同骨质疏松条件下的腰椎生物力学性能差异。方法：采用CT扫描技术获取骨质疏松患者的腰椎断层图像，然后对L4腰椎结构进行三维重建并进行验证。通过改变骨密度，在骨量减少（A1）、中度骨质疏松（A2）、重度骨质疏松（A3）中分别构建两种钉道设计。一种在TT技术中使用传统双螺纹椎弓根螺钉（TT组），直径6mm，全长45mm；另一种在MCBT技术中使用的变径全皮质骨螺纹螺钉（MCBT组），直径4～5.5mm，全长45mm。分析不同骨质疏松条件下，两种钉道设计对螺钉轴向抗拔出力、螺钉稳定性（上、下、左、右工况的载荷位移比，即螺钉尾端向其垂直轴的上、下、左、右位移0.1mm时载荷值与其位移的比值）以及腰椎活动度（前屈、后伸、侧弯及轴向旋转时）的影响。结果：在轴向抗拔出力方面，MCBT组在A1、A2、A3中较TT组分别提高93.5%、96.5%、98.5%。在稳定性方面，上、下、左、右工况在A1、A2、A3下，MCBT组螺钉的载荷位移比，相对于TT组分别提升42.2%、40.8%、41.7%；49%、49%、51.5%；82.4%、81.5%、85.2%；73.1%、70.8%、72.5%。在腰椎活动度方面，前屈时在A1、A2、A3下，TT组较MCBT组增加25%、26.6%、28.7%；后伸时在A1和A2下，TT组比MCBT组增加24.5%、22.9%，而在A3下，差异无显著性意义（P>0.05）；而在侧弯和轴向旋转时，MCBT组在A1、A2、A3下相比TT组仅有轻微增加（P>0.05）。结论：在不同程度骨质疏松分级下，MCBT技术仅在椎体轴向旋转和侧屈时的稳定性上弱于TT技术，但在轴向抗拔出力、螺钉稳定性及椎体前屈、后伸时的稳定性上优于TT技术。

英文摘要:

  【Abstract】 Objectives: To evaluate the difference in biomechanical properties of lumbar spine between traditional trajectory(TT) and modified cortical bone trajectory(MCBT) pedicle screws in different osteoporotic conditions using finite element analysis. Methods：　CT scanning was used to obtain lumbar spinal tomographic images of osteoporotic patients, and then the L4 lumbar spine structure was reconstructed in three dimensions and validated. Two nail channels were constructed by varying the bone density as osteopenia(A1), moderate osteoporosis(A2), and severe osteoporosis(A3), respectively. One was a conventional double-threaded pedicle screw used in TT with a diameter of 6mm and an overall length of 45mm(TT group), the other was a variable-diameter, all-cortical bone threaded pedicle screw used in MCBT with a diameter of 4-5.5mm and an overall length of 45mm(MCBT group). The effects of the two designs on screw pullout resistance, stability(load-displacement ratio of upward, downward, left and right working conditions, defined as the ratio of load value to displacement when screw tail end displaced 0.1mm upward, downward, left and right towards its vertical axis) and lumbar spine mobility(when forward flexion, backward extension, lateral bending and axial rotation) were analyzed under different osteoporotic conditions. Results: In terms of axial pullout force, the MCBT group significantly improved 93.5%, 96.5%, and 98.5% than the TT group in A1, A2, and A3, respectively. In terms of stability, at upward, downward, left, and right working conditions, the load-displacement ratios of the screws in the MCBT group were improved in comparison with the TT group in A1, A2, and A3, respectively, by 42.2%, 40.8%, 41.7%; 49%, 49%, 51.5%; 82.4%, 81.5%, 85.2%; 73.1%, 70.8%, 72.5%. In terms of lumbar spine mobility, at forward flexion, under A1, A2, and A3, the TT group increased by 25%, 26.6% and 28.7% compared to the MCBT group, respectively; at backward extension, the TT group increased by 24.5% and 22.9% compared to the MCBT group under A1 and A2, respectively, whereas under A3, the difference was not significant(P>0.05); at lateral bending and axial rotation, the MCBT group had a slightly slight increase compared to the TT group under A1, A2, and A3(P>0.05). Conclusions: Under different degrees of osteoporosis grading, MCBT technique was inferior in stability to TT technique only in spinal axial rotation and lateral flexion, while it outperformed TT technique in axial pull-out force, screw stability, and spinal stability during forward flexion and backward extension.