椎弓根螺钉置钉深度在胸腰椎骨折矢状面重建中的生物力学作用

目的:探讨和评价椎弓根螺钉不同置钉深度对胸腰椎骨折矢状面重建的生物力学作用.方法:6具新鲜人尸体固定腰段(L_1～L_3节段)脊柱标本,以预损伤方法制作胸腰椎骨折模型.选用直径为6 mm的USS椎弓根螺钉内固定系统,在L_1和L_3椎体各植入2枚Schanz钉,在L_1和L_3前缘正中各植入1枚空心钉,两空心钉根部之间距离设为正常的高度.在椎体前方轴向加载(前负荷),螺钉间的轴向加压模拟撑开复位操作(后负荷).分别在椎体后缘(D1)、椎弓根钉道1/2(D2)和钉道全长(D3)3个置钉深度轴向加载,观测两空心钉根部的直线距离,以后负荷加载至恢复原高度为止,记录椎弓根螺钉置钉深度、骨折椎体高度及后负荷.结果:在3种不同的置钉深度时,随着后负荷的增加,伤椎椎体高度均相应增大,但增加幅度有所不同.当骨折椎体达到完全复位时,D1、D2、D3工况下后负荷分别为 (2 630±13)g、(2 339±61)g和(2 221±164)g.D1与D2之间、D1与D3之间差异有统计学意义(P < 0.01),而D2与D3之间差异无统计学意义(P > 0.05).结论:椎弓根螺钉植入椎体的深度与伤椎复位能力及胸腰椎骨折矢状面重建相关,其植入深度在椎弓根通道1/2至椎弓根通道全长时力学效果最佳.

The Biomechanical Effect of Different Depth of the Pedicle Screw Penetration on the Reconstruction of Spine Sagittal Plane in Thoraco-Lumbar Fracture

Objective: To explore and evaluate the biomechanic relationships between different depth of pedicle screw penetration with the sagittal plane reconstruction in thoracolumbar fracture. Methods:Six fresh cadaveric specimens of lumbar spine from L_1 to L_3 were used to make the model of thoracolumbar fracture. The system of universal spine system( USS )pedicle screw was adopted with the 6 mm diameter of screw. Each of two Schanz screws was implanted into the pedicles of L_1 and L_3 A canulated screw was fixed into the former of vertebral body in L_1 and L_3, and the distance of the two canulated screws was taken as the normal height. The axial loads were given while the pedicle screws were implanted at the depth of D1, D2 and D3, and the distance of the two canulated screw was measured as well as the distance was reduced to the normal height by axial load. The index measured included of the depth of pedicle screw penetration, the height of fractured vertebral body and afterload. Results: Along with the increasing of afterload, the height of injured vertebral body was increased accordingly, but the extent was different at three depth of pedicle screw penetration (D1, D2, and D3). While the injured vertebral body was reduced totally (reduced distance 0.00 mm), there was (2 630±13) g of afterload needed in Dl depth, and (2 339±61) g and(2 221± 164) g of afterload in D2 and D3 depth respectively. There was significant difference in distance between D1, D2 and D3 (P< 0.01), however, no significant difference between D2 and D3 (P> 0.05). Conclusion: There is a relationship in the depth of pedicle screw penetration, the capacity of reduction and sagittal plane reconstruction. The depth of pedicle screw had a significant effect on the capacity of reduction for the injured vertebral body, which would be the best option in biomechanics when the pedicle screw was implanted more than 1/2 pedicle or all of it.