3种不同后路内固定方式及其横连治疗胸腰段骨折的力学性能比较

目的比较3种不同后路内固定方式及其有无横连杆治疗胸腰段骨折的生物力学性能差异,寻找最优化的后路内固定方式。方法在已验证的正常T12~L2有限元模型基础上,模拟L1椎体爆裂性骨折。将T12椎体上半皮质骨切除并赋予内部松质骨损伤材料属性,分别建立无、有横连杆经伤椎单侧螺钉(模型A1、A2)、常规短节段(模型B1、B2)和经伤椎双侧螺钉(模型C1、C2)6种内固定模型。分别比较6组模型在各种生理应力下的活动范围(range of the motion,ROM)以及螺钉和棒的最大Von Mises应力情况。结果在屈伸和侧屈应力下,经伤椎单侧和双侧螺钉内固定模型组ROM均明显小于常规短节段内固定组;而经伤椎单侧和双侧螺钉内固定组,在屈伸应力下两者ROM无显著差异,在侧屈应力下经伤椎双侧螺钉模型的稳定性优于经伤椎单侧螺钉固定。应力主要集中在上位螺钉钉尾和上位螺钉与伤椎螺钉之间的棒体,经伤椎双侧内固定组上位螺钉最大应力明显低于经伤椎单侧和常规短节段内固定组螺钉最大应力。横连可增加各内固定组在扭转应力下的稳定性,也可降低上位螺钉和棒在扭转应力下的最大应力,而屈伸和侧屈应力下螺钉和棒的最大应力未见明显差异。结论经伤椎置钉后路内固定可获得较好的生物力学稳定性,且添加横连不仅能改善构型扭转刚度,而且能降低螺钉和棒的最大扭转应力,是治疗胸腰椎不稳定骨折良好选择。

Comparison of biomechanical properties by different posterior fixation methods with or without crosslink for fixing thoracolumbar fractures

Objective To compare the biomechanical differences in 3 posterior fixation methods with or without crosslink for treatment of thoracolumbar fractures, so as to find the optimal posterior fixation methods. Methods On the basis of the validated finite element model of T12-L2 segments to simulate L1 vertebra burst fracture, the superior 1/2 cortical bone of T12 segment was removed and the superior 1/2 cancellous bone was assigned with the material damage property of cancellous bone. Then 6 thoracolumbar fracture models by intermediate unilateral pedicle screw fixation without or with crosslink (Model A1, A2), traditional short-segment pedicle screw fixation without or with crosslink (Model B1, B2), intermediate bilateral pedicle screw fixation without or with crosslink (Model C1,C2) were established, respectively. The range of motion (ROM) as well as the maximum Von Mises stress of the pedicle screw and rod for 6 models under various physiological loading conditions were compared. Results The ROM under flexion-extension and lateral bending in Model A and Model C was obviously smaller than that of Model B. Under flexion-extension, no significant difference was found in ROM between Model A and Model C; under lateral bending, the ROM of Model C was smaller than that of Model A. The stress was concentrated in the root of upper screw and the rob located between upper screw and intermediate screw; the maximum stress of upper screw in Model C was smaller than that in Model A and Model B. The crosslink could increase the stability of all fixation groups under axial rotation stress condition, and decrease the maximum stress on upper screw and rod under axial rotation stress condition, but no significant difference was found under flexion-extension and lateral bending. Conclusions Additional pedicle screws at the level of fracture vertebra can achieve the better biochemical stability. The additional crosslink not only increases the torsional rigidity, but also decreases the maximum torsional stress of the screw and rod, which is a better choice as the treatment of thoracolumbar fractures.