短节段椎弓根钉固定术的生物力学研究

Biomechanic research on short-segment posterior pedicle screw fixation

目的基于计算机控制的六自由度机器人全新试验装置，更好地模拟人体在自然状态下的复杂运动。比较3椎体4枚、5枚与6枚椎弓根钉固定术治疗胸腰椎爆裂骨折的生物力学稳定性效果。方法采用6具国人新鲜脊柱尸体标本（T11～L3），椎体切除法模拟失去前柱支持、完令不稳定L1椎体爆裂骨折。试验分跨节段3椎体4枚椎弓根钉固定组、3椎体5枚椎弓根钉固定组和3椎体6枚椎弓根钉固定组。应用混合力-位移控制加载的六自由度机器人全新试验装置对标本进行前屈，后伸，左侧弯、右侧弯及左轴向旋转和右轴向旋转6种运动方式，对固定节段（T11～L3）的运动范围（ROM）进行测试并计算刚度值，比较各组间差异：结果随着螺钉数的增加．固定节段（T11～L3）的运动范围逐渐减小，刚度逐渐增大；轴向旋转时，6钉组、5钉组的运动范围小于4钉组（P〈0．05），6钉组刚度大于4钉组（P〈0．05）、5钉组刚度与4钉组的差异无统计学意义（P〉0．05）；6种不同加载方向下，6钉组与5钉组的运动范围与刚度的差异均无统计学意义（P〉0．05）；屈伸、侧弯状态下，3种不同固定方式之间差异不具有统计学意义（P〉0．05）。结论对于胸腰椎爆裂骨折，经骨折椎3椎体6枚钉或5枚钉的固定方式可以提高生物力学稳定性，稳定效果要优下传统的4枚钉固定，而6枚钉与5枚钉固定稳定性的差异不明显。

Objective To compare the stability effect of the fixation segment using the new test system based robotics to simulate the complex human movement at natural state about the three-level fixation by using four, five or six pedicle screws in treatment of thoracolumbar burst fractures. Methods Six human eadaveric spines were dissected from T11 -L3. The inferior half part of L1 vertebral bodies and T11-L2 discs were resected to mimic an unstable L1 burst fracture with loss of anterior column support. Specimens were tested in accordance with the following order： intact, 4,5 and 6 pedicle screws fixation at the three-level fixation. The range of motion （ROM） of the fixation segment （T11 -L3 ） was measured with the six-freedom degree robotics system controlled by mixed force and displacement during flexion, extension, lateral bending and axial torsion, when the stiffness was calculated. One-way statistical analysis was used for analyzing the collected data. Results With increased number of screws, the ROM of the fixation segment （T11-L3 ） was gradually decreased and the stiffness gradually increased. The ROM under axial rotation of six and five screws group became smaller than four screws group （ P 〈 0.05）. The stiffness under axial rotation of six screws group was higher than four screws group （ P 〈 0.05）. There was no statistical difference between five screws group and four screws group in regard of the stiffness in axial rotation （ P 〉 0.05 ）. There were no significant differences in ROM and stiffness under six different loading directions between six screws group and five screws group （P 〉 0.05 ）. No statistical difference was observed for three fixation modes in aspects of ROMs and stiffness under flexion-extension or lateral bending （P 〉 0. 05）. Conclusions Three-level fixation of burst fractures with five or six screws offers improved biomechanical stability compared with traditional four screws fixation. But the difference is insignificant between six and five screws fixations.