Objective: To investigate the biomechanical properties of H-shaped and L-shaped miniplate fixation systems (H-MFS and L-MFS, respectively) in restorative laminoplasty for spinal canal reconstruction (RL-SCR).
Methods: Laminectomy was performed in a 3D printed L4 vertebral model followed by RL-SCR using H-MFS or L-MFS, and the biomechanical properties of the reconstructed models were evaluated using static and dynamic compression tests. Biomechanical analyses of RL-SCR were also conducted in finite element models of the L3-L5 vertebrae with normal assignment (NA), laminectomy, or fixation with H-MFS or L-MFS, and the range of motion (ROM) of L3-L4 and L4-L5 was evaluated.
Results: In static compression test, the sustained yield load, compression stiffness, yield displacement and axial displacement- axial load were all significantly greater in H-MFS group (P < 0.05). Door closing, lamina collapse and plate breakage occurred in all the models in L-MFS group, and only some models in H-MFS group showed plate cracks and screw loosening. In dynamic compression tests, the peak load in H-MFS group reached 873 N (which was 95% of the average yield load in static compression), significantly greater than that in L-MFS group (P < 0.05). The ultimate load in L-MFS group was only 46.59% of that in H-MFS group (P>0.05). In finite element analysis, the ROM of the L3-L4 and L4- L5 segments were significantly smaller in NA, H-MFS and L-MFS groups than in laminectomy group. Compared with NA group, H-MFS group showed a greater ROM during extension, and L-MFS group showed greater ROM in flexion, extension, bending, and rotation; The overall ROM of the vertebral segments decreased in the order of laminectomy group, L-MFS group, H-MFS group, and NA group.
Conclusion: Laminectomy causes structural destruction of the posterior column of the spine to affect its biomechanical stability. RL-SCR can effectively maintain the biomechanical stability of the spine, and H-MFS is superior to L-MFS in maintaining the integrity and biomechanical properties of the reconstructed spinal canal.
目的: 比较椎板切除回植后应用不同钢板内固定系统(微H钢板和微L钢板)重建椎管的生物力学性能。
方法: 应用3D打印技术打造正常腰4(L4)椎体模型，对L4椎体模型实施全椎板切除，根据椎板回植椎管重建(RL-SCR) 内固定方式的不同分成微H钢板(H-MFS)组和微L钢板(L-MFS)组；分别通过静态压缩和动态疲劳压缩实验对两组RL-SCR模型进行加载直至钢板失效、断裂或回植椎板塌陷；静态压缩实验采用速度控制模式，动态疲劳压缩实验采用载荷控制模式。同时，通过建立正常L3- L5有限元模型，在验证该模型有效性的前提下进行RL-SCR的生物力学研究；根据处理方式不同分为正常赋值组、椎板切除组、H-MFS组和L-MFS组；在相同载荷下，模拟前屈、后伸、左弯、右弯、左旋和右旋6个方向的生理活动条件，对各组L3-L4和L4- L5的活动度(ROM)变化进行评估。
结果: RL-SCR静态压缩实验中，H-MFS组的持续屈服载荷大于L-MFS组(P < 0.05)，在相同机械载荷下的压缩刚度、屈服位移和轴向位移-轴向载荷排列为：H-MFS组>L-MFS组(P < 0.05)；L-MFS组全部出现椎板原位还纳或“闭门”现象及椎板塌陷，均出现钢板断裂现象；而H-MFS组未出现钢板断裂现象，仅部分出现螺钉周围的钢板裂纹和螺钉尾帽松动的现象；RL-SCR的动态压缩疲劳实验中，H-MFS组的动态压缩峰值载荷可达873 N，为静压缩平均屈服载荷的95%，优于L-MFS组(P < 0.05)；而L-MFS组的动态压缩峰值荷载仅为468 N，为静压缩平均屈服载荷的80%；此外，根据疲劳寿命-峰值载荷图估算出L-MFS组的极限载荷仅为H-MFS组的46.59%，差异有统计学意义(P < 0.05)。与椎板切除组相比，6种加载工况下，正常赋值组、H-MFS组和L-MFS组L3-L4和L4-L5的ROM范围均明显降低；与正常赋值组相比，H-MFS组仅在后伸时的ROM增加明显，而L-MFS组在前屈、后伸、左旋和右旋时的ROM增加明显；病变节段ROM的整体趋势为椎板切除组>L-MFS组>H-MFS组>正常赋值组。
结论: 椎板切除会破坏脊柱后柱结构，从而影响其生物力学稳定性，而应用RL-SCR内固定的方式可有效维持脊柱生物力学的稳定性，且与微L钢板相比，微H钢板在维持椎管完整性和生物力学性能上的优势更明显。
Keywords: biomechanics; dynamic compression; finite element analysis; lamina replantation; restorative laminoplasty for spinal canal reconstruction; static compression; threedimensional printing.