椎弓根螺钉不同固定方法治疗胸腰椎骨折的生物力学分析

Biomechanical analysis of different fixation methods of pedicle screws for thoracolumbar fracture

背景:胸腰椎骨折经皮内固定已较为成熟,目前临床固定方式较多,但由于缺乏一种能同时兼顾力学效应和可操作性的固定方式,导致临床疗效各有差异。目的:观察不同椎弓根螺钉内固定组合形式下椎体的生物力学特性。方法:采用新鲜猪腰椎多节段椎骨标本24例,随机分为8组并造模:A1、A2组采用经伤椎6枚万向钉固定,B1、B2组采用4枚单向钉联合经伤椎2枚万向钉混合固定,C1、C2组采用经伤椎6枚单平面螺钉固定,D1、D2组采用跨伤椎4枚单向钉固定。然后利用万能试验机测定8组内固定方式的生物力学情况,A1、B1、C1、D1组行静态实验,A2、B2、C2、D2组行疲劳实验。结果与结论:①4组内固定均能对腰椎骨折进行有效固定,伤椎置钉组的最大载荷均明显高于伤椎未置钉组;载荷最大的为C1组,最小的为D1组,且4组数据之间差异均有显著性意义(P<0.05);②A1、B1、C1、D1组行加压撑开实验,B1、C1、D1组均完成了3次撑开实验,A1组在加压300 N时出现钉尾的滑移终止实验;C1组的复位效果优于A1、B1、D1组,差异有显著性意义(P<0.05);B1组的复位效果优于A1、D1组,差异有显著性意义(P<0.05);A1与D1组复位效果相当,差异无显著性意义;③统计4种内固定系统载荷前后椎体前缘高度变化,组内比较,载荷后B2、C2、D2组椎体前缘高度与载荷前相比差异无显著性意义;载荷后A2组椎体前缘高度较载荷前明显降低,差异有显著性意义(P<0.05);④提示3种椎弓根螺钉均可以承载胸腰椎大部分应力,伤椎置钉方式能提供更有效的稳定性,伤椎形态恢复更好,其中单平面螺钉的内固定效果优于其他3种内固定螺钉置入方式。

BACKGROUND:Percutaneous fixation of thoracolumbral and lumbar fractures has been relatively mature,and there are many clinical fixation methods at present.However,due to the lack of a fixation method that can take the mechanical effect and operability into account,the clinical efficacy is different.OBJECTIVE:To study the biomechanical properties of lumbar vertebrae under the different kinds of pedicle screw fixation.METHODS:Twenty-four cases of fresh multi-segment lumbar vertebrae of pigs were randomly divided into eight groups and modeled:groups A1 and A2 were fixed with six universal screws;groups B1 and B2 were fixed with four one-way screws and two universal screws;groups C1 and C2 were fixed with six uniplanar pedicle screw;groups D1 and D2 were fixed with four one-way screws.The biomechanics of eight groups was measured by universal testing machine.Four groups of A1,B1,C1 and D1 performed static experiments,while A2,B2,C2 and D2 performed fatigue experiments.RESULTS AND CONCLUSION:(1)All the four internal fixations could effectively fix lumbar fractures.The maximum load of the screw fixation at the fracture level was significantly higher in the screw placement group than that of unscrew placement group.Group C1 had the largest load,and group D1 had the smallest load,and there were significant differences among the four groups(P<0.05).(2)Groups A1,B1,C1 and D1 conducted pressurized buttoning experiments,and the three groups B1,C1 and D1 all completed the buttoning experiments three times.The A1 group showed the slip of the nail tail when pressurized 300 N.The reduction effect of group C1 was better than that of groups A1,B1 and D1,and the difference was statistically significant(P<0.05).The reduction effect of group B1 was better than that of groups A1 and D1,and the difference was statistically significant(P<0.05).There was no significant difference in reduction effect between groups A1 and D1.(3)There was no significant difference in the anterior vertebral body height in groups B2,C2 and D2 after loading compared with that before loading.After loading,the anterior vertebral body height in group A2 was significantly lower than that before loading(P<0.05).(4)All three kinds of pedicle screws can bear most of the stress of thoracolumbar vertebra,and the screw placement mode of injured vertebra can provide more effective stability and better shape recovery of injured vertebra.The effect of the uniplanar pedicle screw is better than that of the other three fixation screws.