椎体内裂隙的位置和程度影响伤椎稳定性的生物力学分析

Biomechanical effects of location and extent of intravertebral vacuum cleft on the stability of osteoporotic vertebrae

目的分析椎体内真空裂隙(intravertebral vacuum cleft,IVC)的位置和程度变化对胸腰椎稳定性的影响。方法在已验证的T11~L1有限元骨质疏松模型的基础上,指定T12为伤椎,结合既往文献报道将T12椎体内部松质骨在不同位置予以不同程度的截除,模拟9种IVC的有限元模型。首先将前1/2高2 mm松质骨在偏上、中、偏下予以截除模拟轻度IVC模型(S1、C1、I1),将前1/2高4 mm松质骨截除模拟上下进展的重度IVC模型(S2、C2、I2),将高2 mm松质骨完整截除模拟前后进展的重度IVC模型(S3、C3、I3)。分别比较9种模型在各种生理活动范围时在T12皮质骨应力分布差异。结果对所有IVC模型而言,最大米塞斯应力(von Mises)主要集中在前屈活动时伤椎皮质骨前壁上下缘,其次是后伸活动时后壁上下缘。当IVC偏上或偏下时,伤椎皮质骨最大应力在前屈时显著增加(超过正常模型17%),而当IVC位于中部时最大应力仅轻微增加(约超过正常模型5%)。当IVC进展性加重时,模型的最大应力均增加,但是当IVC向前后进展加重时在各种生理活动范围下最大应力值超过轻度IVC模型最大应力8%以上,而当IVC上下进展加重时最大应力值仅超过轻度IVC模型最大应力值3%以下。结论除IVC位于中部时对伤椎稳定性影响较小外,其余大部分位置和程度的IVC对伤椎稳定性均有显著的影响,可能需要早期手术干预以稳定椎体、预防进展性严重塌陷。

Objective To investigate the biomechanical effects of location and extent of intravertebral vacuum cleft（ IVC） on the stability of osteoporotic vertebrae. Methods Based on previous studies and our established and validated osteoporotic T11 ～ L1 finite element（ FE） model,9 IVC FE models in T12 were simulated stepwise. Firstly,the anterior half of cancellous bone with 2 mm in height was resected in different locations adjacent to superior（ S） or inferior（ I） endplate or in the central（ C） of vertebral body,resulting in3 mild IVC models（ S1,C1,I1）. Then,the mild IVC models were developed to 6 types of severe IVC by extended resection of the cancellous bone toward either superoinferior（ S2,C2,I2） or anteroposterior（ S3,C3,I3） direction. The magnitudes and distributions of the von Mises stress in cortical bone of the 9 simulated IVC models as well as intact model were evaluated under all physiologic conditions of loading. Results For all IVC models,the maximum von Mises stress appeared in the anterior wall under flexion,followed byposterior wall under extension. In the mild IVC models,the von Mises stress was remarkably increased by at least 17% compared to the intact model when the IVC was adjacent to endplates under flexion. But the increase was. 5% when IVC was located centrally in vertebral body. Furthermore,the maximum stress was increased along the progression of mild to severe IVC models. While less than 3% of maximum stress magnitude increased in the mild model when the extent of IVC expanded toward superoinferior direction in anterior column,more than 8% was increased in the severe IVC model when expanded to the middle column under all the physiological loadings. Conclusion Except the central IVC,the majority of IVC models stimulated by varied locations and extents can cause significant instability of injured vertebrae,and thus early vertebral augmentation is required for vertebral stability and prevention of progressive collapse.