构建3D椎体模型比较经皮椎体后凸成形与经皮椎体成形治疗胸腰椎压缩性骨折的力学变化

Mechanical changes of percutaneous kyphoplasty and percutaneous vertebroplasty in the treatment of thoracolumbar compressive fractures in three-dimensional vertebral models

背景:老年人胸腰椎骨折与一般骨折相比有不同的病理变化,多伴有其他全身疾患。较常用的手术方法为经皮椎体成形和经皮椎体后凸成形,不同的术式选择与术后再骨折发生率有关,而如何选择有效的内固定系统及治疗方式对减少老年胸腰椎骨折手术固定失败至关重要。目的:在3D椎体模型上构建压缩性骨折胸腰椎模型,分析腰椎压缩性骨折的力学变化特点。方法:选择1例56岁男性腰痛患者(后确诊为腰肌劳损),椎体形态无明显异常;1例54岁男性由于骨质疏松导致的胸腰椎压缩性骨折患者,2例患者对实验方案知情同意,且得到医院伦理委员会批准,均获取T12-L1节段CT资料。根据腰痛志愿者CT数据,利用Mimics 10.0软件建立椎体3D数字模型,利用三维有限元分析软件Ansys 12.0建立椎体3D实体模型。参照骨折患者资料对正常椎体有限元模型中的L1模拟椎体压缩性骨折,并在此基础上模拟经皮椎体后凸成形和经皮椎体成形手术过程,记录不同载荷下模型各部分Von Mises应力以及变形。结果与结论:(1)与其他作者体外生物力学测试实验结果比较,此模型的实验结果与其基本一致(P>0.05);(2)经皮椎体后凸成形模型在直立及前屈、后伸、侧弯及右旋荷载下,T12与L1节段变形均显著小于术前及经皮椎体成形模型(P<0.05);经皮椎体成形模型的骨折节段T12与L1在各种荷载下的脊椎变形与术前差异无显著性意义(P>0.05);(3)经皮椎体后凸成形模型骨折节段T12与L1在直立及前屈、后伸、侧弯及右旋荷载下的最大应力较术前及经皮椎体成形模型显著减小(P<0.05);经皮椎体成形模型的骨折节段T12与L1在各种荷载下最大应力与术前差异无显著性意义(P>0.05);(4)提示经皮椎体后凸成形在直立及前屈、后伸、侧弯及右旋荷载下,T12与L1节段变形及应力均显著小于术前的压缩性骨折模型及经皮椎体成形治疗模型,表明经皮椎体后凸成形可显著增加脊柱胸腰段刚度,经皮椎体成形对于胸腰段刚度无明显影响。

BACKGROUND:Compared with general fractures,thoracolumbar fractures in the elderly have different pathological changes and are often accompanied by other systemic diseases.Percutaneous vertebroplasty and percutaneous kyphoplasty are the most commonly used surgical methods.The choice of different surgical methods is related to the incidence of re-fracture after operation.How to choose an effective internal fixation system and surgical methods is very important to reduce the failure of surgical treatment of thoracolumbar fractures in the elderly.OBJECTIVE:To study and compare the finite element mechanics of lumbar vertebral compression fracture by establishing 3D vertebral digital model and thoracolumbar compression fracture model.METHODS:A 56-year-old male patient with low back pain(later diagnosed as lumbar muscle strain)had no abnormal vertebral shape and a 54-year-old male patient with thoracolumbar vertebral compression fracture induced by osteoporosis were selected in this study.The two patients signed informed consent.This study was approved by the Hospital Ethics Committee.CT data of T12-L1 segments were obtained.Based on CT data of volunteers with low back pain,a three-dimensional digital model of vertebral body was established by using Mimics 10.0 software.Three-dimensional finite element analysis software Ansys 12.0 was used to establish the three-dimensional solid model of the vertebral body.L1 of vertebral compression fracture in finite element model of normal vertebral body was simulated with reference to fracture patient data.On this basis,the procedures of percutaneous vertebroplasty and percutaneous kyphoplasty were simulated to record Von Mises stresses and the deformation of different parts of the model under different loads.RESULTS AND CONCLUSION:(1)Compared with the results of in vitro biomechanical test,the experimental results of this model were basically consistent with those of in vitro(P>0.05).(2)Under vertical and forward bending,backward extension,lateral bending and right-handed loads,the deformations of T12 and L1 were significantly smaller in percutaneous kyphoplasty models than those of preoperative compressive fracture models and percutaneous vertebroplasty treatment models(P<0.05).There was no significant difference in the spinal deformations of T12-L1 under various loads between percutaneous vertebroplasty models and preoperative models(P>0.05).(3)The maximum stress of T12 and L1 was significantly lower in percutaneous kyphoplasty models than in preoperative models and percutaneous vertebroplasty models under vertical and forward bending,backward extension,lateral bending and right-handed loads(P<0.05).There was no significant difference in the maximum stress of T12 and L1 between percutaneous vertebroplasty models and preoperative models under various loads(P>0.05).(4)The deformation and stress of T12 and L1 segments of percutaneous kyphoplasty models were significantly less than those of preoperative compressive fracture models and percutaneous vertebroplasty models under vertical and forward bending,backward extension,lateral bending and right-handed loads.These suggest that percutaneous kyphoplasty can significantly increase the thoracolumbar stiffness of the spine,while percutaneous vertebroplasty has no significant effect on the thoracolumbar stiffness.