短节段椎弓根钉固定术对相邻椎间盘影响的生物力学研究

Effects of short-segment posterior pedicle fixations on adjacent intervertebral discs： a robotics-based biomechanicai research

目的比较跨节段3椎体4枚、经骨折伤椎3椎体5枚及3椎体6枚椎弓根钉固定治疗胸腰椎爆裂性骨折对相邻椎间盘应变的影响，为临床术式选择提供力学依据。方法采用6具国人新鲜脊柱尸体标本（T11～L3），模拟失去前柱支持的完全不稳定L1椎体爆裂性骨折。实验分三组：跨节段固定组（4枚钉组）、5枚钉组和6枚钉组。每个标本依次进行完整状态、跨节段3椎体4枚椎弓根钉固定状态（4枚钉组）、3椎体5枚椎弓根钉固定状态（5枚钉组）、3椎体6枚椎弓根钉固定状态（6枚钉组）的试验测试。应用混合力-位移控制加载的六自山度机器人实验装置对标本施加前屈，后伸，左、右侧弯及左、右轴向旋转6种运动方式，测试上、下相邻椎间鼎的应变，比较三组间差异。结果随着螺钉数的增加，固定节段相邻椎间盘（T11,12、L2,3）应变逐渐增大。上位相邻椎间盘（L11,12）仅在轴向旋转状态下，6枚钉组和5枚钉组与4枚钉组比较差异均有统计学意义（P〈0．05），6枚钉组与5枚钉组间差异无统计学意义（P〉0．05）；其他状态下二组差异均无统计学意义（P〉0．05）。固定节段下位相邻椎间盘（L2-3）任何状态下两两比较差异均无统计学意义（P〉0．05）。结论跨节段3椎体4枚椎弓根钉、经骨折椎3椎体5枚椎弓根钉、经骨折椎3椎体6枚椎弓根钉固定治疗胸腰椎爆裂性骨折，随着螺钉数的增加，邻近椎间盘应变增加，且上位相邻椎间盘廊变增加更为明最，其退变的可能性大于下位相邻椎间盘。

Objective To compare the effects of three-level fixations by 4, 5 and 6 pedicle screws into the adjacent upper and lower vertebrae on the strain changes at the adjacent intervertebral discs in the treatment of thoracolumbar burst fractures. Methods Six human cadavcric spines were dissected to prepare specimens of TI1-L3. The inferior half of the L1 vertebral bodies and L1-L2 discs were resected to simulate an unstable L1 burst fracture without support of anterior column. Biomechanical tests were performed in groups of intact condition and three-level fixations by 4, 5 and 6 pedicle screws. The strain changes at T11/12, L2/3 disc were measured by a robotic system of 6 degrees of freedom under loadings at flexion, extension, the left and right lateral bendings, and the left and right axial torsions. One-way statistical analysis was used to compare the data collected. Results With the increase in number of screws, the strain at the adjacent intervertebral discs （T11/12, L2/3） was gradually increasing. The strains at T11/12 disc in fixations by 5 and 6 screws were significantly lager than in fixation by 4 screws only under axial rotation （P 〈 0. 05）, but there were no significant differences between fixations by 5 and 6 screws （ P 〉 0.05 ）. The strains at L2/3 disc were not significantly different among the 3 groups under any loading （ P 〉 0.05 ） . Conclusions In the three-level fixations by 4, 5 and 6 pedicle screws to treat thoracolumbar burst fractures, strains at the adjacent intervertebral discs may be gradually increasing with the increase in number of screws. Since the strain at the adjacent upper intervertebral disc is increased more markedly, the upper disc is more likely to degenerate than the lower disc.