全脊椎截骨重建强直性脊柱后凸矢状面平衡的有限元分析

Finite element analysis of reconstruction of sagittal balance in ankylosing kyphosis with vertebral column resection

背景:过去强直性脊柱后凸矫形往往注重局部畸形的矫正,忽略对于矢状面平衡的重建。目的:应用计算机辅助软件建立强直性脊柱炎后凸三维有限元模型,基于肺门-髋轴法重建脊柱矢状面平衡,设计个性化手术截骨方案,并模拟全脊椎截骨手术操作,计算分析其生物力学特性,并与两种未重建脊柱矢状面平衡模型进行对比。方法:收集来自新疆医科大学第六附属医院1例强直性脊柱炎后凸住院患者的CT数据,根据301分型确定后凸畸形为ⅢA型,将CT数据导入计算机建模软件中,建立强直性脊柱后凸畸形三维有限元模型。设计3种不同全脊椎截骨(VCR)手术方案的模型,分别为VCR30°,VCR32.2°和VCR40°,其中VCR32.2°使用肺门-髋轴测量方法测量L3预截骨角度为32.2°,另外构建2个未重建脊柱矢状面平衡模型,其中VCR30°设置为截骨角度为30°,VCR40°设置截骨角度为40°,在构建完成的3个模型上模拟全脊椎截骨术进行截骨,并对截骨矫形后3个模型的脊柱位移、钉棒系统、钛笼和截骨面进行有限元计算。结果与结论:①总位移和24个椎体位移大小排序如下:VCR40°>VCR30°>VCR32.2°,VCR40°明显高于VCR32.2°,VCR30°和VCR32.2°两者由于截骨角度差异小,位移差距不显著;椎弓根螺钉、钛棒、钛笼以及截骨接触面的应力分布趋势;②不论是钉棒应力,还是钛笼应力,VCR40°都要高于其他2个模型和平均值,并且差异明显,VCR32.3°在3种模型中应力最小,也低于平均值,并且各节段等效应力分布均匀,没有出现应力集中的现象;③结果证实,基于肺门-髋轴法重建脊柱矢状面平衡能够增加术后脊柱稳定性,且内固定应力分布更低,是一种合理、科学的手术方案设计。

BACKGROUND:In the past,the correction of ankylosing kyphosis often focused on the correction of local deformities,ignoring the reconstruction of sagittal balance.OBJECTIVE:To establish a three-dimensional finite element model of ankylosing spondylitis kyphosis by using computer-aided software,design a personalized osteotomy scheme based on the reconstruction of sagittal balance of spine by hilum hip axis method,simulate the operation of vertebral column resection(VCR),calculate and analyze its biomechanical characteristics,and compare with two kinds of sagittal balance models without reconstruction.METHODS:CT data of an inpatient from the Sixth Affiliated Hospital of Xinjiang Medical University were collected.According to 301 classification,kyphosis was identified as ⅢA.The CT data were imported into computer modeling software to establish a three-dimensional finite element model of ankylosing kyphosis.Three different surgical models were designed,which were VCR30°,VCR32.2°and VCR40°,in which VCR32.2°was used to measure the pre osteotomy angle of L3,which was 32.2°using the measurement method of hilum hip axis.In addition,two non-reconstructed spinal sagittal plane balance models were constructed,in which VCR30°was set as the osteotomy angle 30°and VCR40°was set as the osteotomy angle 40°to simulate VCR in the three models.The spinal displacement,screw rod system,titanium cage and osteotomy surface of the three models were calculated by finite element method.RESULTS AND CONCLUSION:(1)The order of total displacement and displacement of 24 vertebral bodies was VCR40°>VCR30°>VCR32.2°;VCR40°was significantly higher than VCR32.2°;VCR30°and VCR32.2°had no significant displacement difference due to the small difference of osteotomy angle.(2)The stress distribution trend of pedicle screw,titanium rod,titanium cage and osteotomy contact surface:no matter titanium rod or titanium cage,VCR40°was higher than the other two models and the average,and the difference was significant.VCR32.3°had the smallest stress in the three models,and was lower than the average value.The equivalent stress distribution of each segment was uniform,and there was no stress concentration.(3)Results confirmed that reconstruction of sagittal balance of spine based on hilum hip axis method can increase postoperative spinal stability,and lower stress distribution of internal fixation,which is a reasonable and scientific surgical design.