脊柱胸腰段应力分布与骨折相关性的三维有限元分析

A three-dimensional finite element analysis of correlations between stress distribution and fracture in the thoracolumbar spine

中文关键词:  椎体骨折  胸腰段脊柱  三维有限元模型  应力分析

英文关键词:Vertebral body fracture  Thoracolumbar spine  Three-dimensional finite element model  Stress analysis

中文摘要:

  【摘要】 目的：观察脊柱胸腰段骨折与椎体骨性结构及韧带间应力分布的相关性，探索脊柱胸腰段椎体骨折的力学机制。方法：招募8名健康男性青年志愿者，行脊柱全长X线片和CT检查排除脊柱畸形、肿瘤及骨病，对脊柱各椎体及股骨行骨密度测定排除骨质疏松。均行自T11椎体上终板至L2椎体下缘CT薄层扫描，将8名志愿者CT图像参数导入ABAQUS 2016软件中进行标准化，并进行有限元网格化构建。应用MIMICS 17.0、GEOMAGICS 15.0和PRO/ENGINEER 5.0软件处理，建立脊柱胸腰段有限元模型，测量模型相关参数，并验证模型有效性。在T11椎体上终板上加载竖直轴向载荷500N、附加扭矩10N·m模拟垂直压缩、前屈、后伸、左右侧屈、左右旋转7种运动状态，使用ABAQUS软件对有限元模型7种运动状态下的应力分布特点及变化规律进行分析，观察应力分布与脊柱胸腰段骨折的相关性。结果：建立的三维有限元模型共有309583个节点和428760个单元，包括4个椎体、3个椎间盘、前纵韧带、后纵韧带、横突间韧带、棘间韧带等结构。7种运动状态下的数据与文献报道的数据无明显偏差，模型有效。T11~L2椎体椎弓根截面积分别为135mm2、154mm2、105mm2、139.2mm2。应力云图结果显示各运动状态下高应力区存在于椎体的松质骨、椎弓根及其周围骨皮质。在垂直压缩状况下，T12椎体所受应力最大（617.4MPa），前屈状态下T11所受应力最大（200.7MPa），后伸、左右侧屈和左右旋转状态下L1椎体所受应力最大（314.2MPa、574.4MPa、626.2MPa、641.3MPa、527.1MPa），且前屈体位时椎体所能承受的应力最小，左旋转时所能承受的应力最大。垂直压缩状况下T12椎体发生骨折， 前屈状态下T11发生骨折伴韧带损伤，后伸、左右侧屈和左右旋转状态下L1椎体发生骨折伴韧带损伤。骨折发生时，前纵韧带在后伸、左右侧屈状态下存在高应力区，后纵韧带在前屈状态下存在高应力区，横突间韧带和棘间韧带在前屈、左右侧屈、左右旋转状态下存在高应力区。结论：在构建包括重要韧带、椎间盘等软组织结构的脊柱胸腰段三维模型中，椎体松质骨、椎弓根及其周围骨皮质、韧带均存在高应力区，不同状态下所受应力最大椎体不同，发生骨折的椎体和韧带损伤也不同；L1椎弓根截面积最小，最易发生骨折。

英文摘要:

  【Abstract】 Objectives: To observe and analyze the relationship between thoracolumbar vertebral fractures and vertebral bone structure, as well as stress distribution within ligaments, in order to explore the mechanical mechanisms underlying thoracolumbar vertebral fractures. Methods: Eight healthy young male volunteers were recruited for the study. X-ray and CT examinations of the entire spine were conducted to rule out spinal deformity, tumor, and bone disease. Bone mineral density(BMD) measurements were taken for each vertebral body and femur to exclude osteoporosis. CT thin layer scan was performed from the upper endplate of T11 to lower edge of L2 vertebra, and the CT image parameters were imported to ABAQUS 2016 software to standardize and perform finite element mesh construction. The thoracolumbar spine finite element model was developed using MIMICS 17.0, GEOMAGICS 15.0, and PRO/ENGINEER 5.0 softwares to measure relevant parameters, and its efficacy was validated. Seven motion states, including vertical compression, flexion, extension, left and right lateral bending, and left and right rotation, were simulated. ABAQUS software was employed to analyze stress distribution patterns and variations in the seven motion states of the finite element model, allowing for the observation of the relationship between stress distribution and thoracolumbar fracture. Results: The validated three-dimensional finite element model utilized in this study consisted of 309,583 nodes and 428,760 elements, encompassing anatomical structures such as four vertebral bodies, three intervertebral discs, and various ligaments including the anterior longitudinal ligament, posterior longitudinal ligament, intertransverse ligament, and interspinous ligament. Analysis of the data across seven different motion states revealed no significant deviations from the findings reported by other literature, confirming the accuracy and reliability of the model. The cross-sectional areas of T11-L2 pedicle were 135mm2, 154mm2, 105mm2, and 139.2mm2, respectively. High stress areas presented within the cancellous bone of the vertebral body, the pedicle and surrounding cortex of the vertebral body during various states of motion according to the stress cloud map analysis. Specifically, the T12 vertebral body exhibited the highest stress level(617.4MPa) under vertical compression, while the T11 vertebral body experienced the highest stress level(200.7MPa) during forward flexion. Additionally, the maximum stress levels recorded for the L1 vertebral body were 314.2MPa, 574.4MPa, 626.2MPa, 641.3MPa, and 527.1MPa during extension, left and right lateral bending, and left and right rotation, respectively. The stress experienced by the L1 vertebral body was found to be minimal in the flexion position and maximal in the left rotation position. T12 vertebral fracture was observed under vertical compression, while T11 vertebral fracture occurred during flexion. L1 vertebral fracture, in combination with ligament injury, was observed during extension, left and right lateral bending, and left and right rotation. High stress areas were identified in anterior longitudinal ligament during extension and left and right lateral bending and in posterior longitudinal ligament during flexion. High stress areas were observed in the intertransverse and interspinous ligaments during movements involving forward flexion, left and right lateral bending, and left and right rotation. Conclusions: In the three-dimensional model of thoracolumbar spine, incorporating key ligaments, intervertebral discs, and other soft tissue structures, notable areas of high stress were identified within the cancellous bone of vertebral body, pedicle and surrounding cortical bone, and ligaments. Variations in maximum stress levels were observed in vertebral body under different conditions, resulting in varying degrees of vertebral body fracture and ligament injury; L1 pedicle exhibited the smallest cross-sectional area and was prone to fracture.