有限元动态仿真建立8岁儿童颈椎关节突关节模型

Establishment of finite element dynamic simulation models of cervical spine facet joint in a 8-year-old child

背景:学龄期儿童并非等比例的"小成人",其颈椎的形态发育、生理特性和力学变化等并非成人的比例性缩小,均有其自身的特征和规律。颈椎的各关节突关节承受着颈椎一定范围内的前屈、后伸、压缩、牵拉、剪切、扭转等负荷,此结构特征是颈椎的运动枢纽,对维持颈椎稳定及正常生理活动起着至关重要的作用。目的:建立1例8岁儿童全颈椎(包括椎间盘、软骨、韧带)仿真动态有限元模型,分析C2-7关节突关节在6个动态工况下及不同椎序间的载荷及应力大小分布,探讨其关节突动态受力对颈椎运动承载的贡献,预测在不同运动状态下颈椎发生损伤的风险、部位与关节突受力特点的相关性,同时也为儿童颈椎各种有限元的应用提供有效建模方法。方法:选取1例经甲醛固定的无明显外伤畸形新鲜8岁男童颈椎标本(由内蒙古医科大学解剖志愿者遗体捐献室提供),体质量30kg;行全颈椎64排CT高分辨率扫描,层厚0.625mm图像以DICOM格式导入Mimics16.0软件行全颈椎椎骨、椎间盘、韧带的3D模型建立,优化并划分网格,将Mimics软件保存生成的inp格式文件导入到Abaqus软件中。经参考各文献分析对颈椎不同解剖结构的有限元模型赋予材质属性后在6个动态工况下加载(除韧带使用Abaqus中的Truss单元进行模拟),分析其C2-7关节突应力云图。结果与结论:有效建立了仿真动态有限元模型,对指导学龄期儿童颈部发育保健、生理活动、医学诊疗及运动康复有重要现实意义。仿真模拟建立儿童颈椎关节突的动态应力变化模型,左、右侧关节突在左屈、右屈时75%Mises应力分布大小有显著差异,前屈、后伸、左旋、右旋时左右侧关节突应力值无统计学意义,不同椎序间关节突应力对整个颈椎的贡献也不尽相同(不同状态上下关节突、同一关节突背腹侧、左右侧都有区域性差异)。

BACKGROUND:School-age children are not equal proportion of"small adults".Their cervical vertebra morphological development,physiological characteristics and mechanical changes are not proportional to adult shrinking;all have their own characteristics and rules.The facet joints of the cervical vertebrae(hereinafter referred to as"cervical facets")bear the load of flexion,extension,compression,pull,shear and torsion within a certain range of cervical vertebrae.This structure is characterized by the movement of the cervical spine.It plays an important role in maintaining the stability of cervical spine and normal physiological activity.OBJECTIVE:A dynamic finite element model of the whole cervical vertebra(including intervertebral disc,cartilage and ligament)was established in an 8-year-old child.The load and stress distribution of C2-7 facet joints were analyzed under six dynamic conditions and between different vertebrae.This study aims to investigate the contribution of dynamic stress on cervical spine movement,to predict the risk of cervical spine injury under different motion conditions,and to predict the correlation between the position and the stress characteristics of the joint process,and to explore the finite element mechanics of cervical vertebra in the child.METHODS:A fresh 8-year-old boy cervical spine specimen fixed by formalin(no obvious trauma deformity,provided by the Body Donation Room of Anatomy Volunteers of Inner Mongolia Medical University),weighing 30 kg,was selected.The whole cervical spine was scanned with 64-slice CT high-resolution,and the images of 0.625 mm slice thickness were imported into Mimics 16.0 software in DICOM format to establish,optimize and mesh the 3D models of the whole cervical vertebrae,intervertebral discs and ligaments.The Mimics software saved the generated inp format file to import into the Abaqus software.Materials assigned to finite element models of different anatomical structures of cervical vertebrae by reference to literature analysis Attributes were loaded under six dynamic conditions(the ligaments were simulated with the Truss unit in Abaqus),and the stress profiles of C2-7 joints were analyzed.RESULTS AND CONCLUSION:This study effectively established the dynamic finite element model of simulation,which had important practical significance for guiding the neck development and health care,physiological activities,medical diagnosis and treatment and sports rehabilitation of school-age children.The dynamic stress model of the cervical vertebrae process in the child was established by simulation.There was significant difference in the distribution of 75%Mises stress between left and right articular processes,including anterior flexion,extension,and left rotation.The stress value of the left and right articular process was not statistically significant,and the contribution of the stress to the whole cervical vertebrae was different among different intervertebral sequences(different states of the upper and lower articular process,the same ventral articular process,regional difference between the left and the right).