三维有限元法分析先天性脊柱侧凸冠状面腰骶段的柔韧性

Flexibility of the coronal lumbosacral region of congenital scoliosis:a three-dimensional finite element analysis

背景:先天性脊柱侧凸患者脊柱运动单元发育存在缺陷,椎体活动柔韧性相对较差,在临床工作中发现此类患者冠状面腰骶段(L_4-S_1)的脊柱代偿能力和术后是否会出现不可自行代偿的躯干偏移存在一定关联。目的:建立正常人和先天性脊柱侧凸患者冠状面腰骶段不同柔韧性的三维有限元模型,通过比较3种模型在不同载荷下的形变、位移、应力和刚度等力学数值变化而完成有限元分析。方法:分别以1名正常人和术前冠状面腰骶段柔韧性不同(随访中是否发生不可代偿的躯干偏移)的2名先天性脊柱侧凸患者为建模样本,通过螺旋CT扫描获得腰骶段DICOM格式的图像数据,将其导入到三维重建软件MIMICS中,根据选取CT图像中各组织的灰度值不同,通过阈值来提取相应的组织,生成3D模型,并将通过GEOMAGIC进行简化处理后的腰骶段三维模型导入到有限元软件ABAQUS中进行不同载荷状态下的力学指标分析。结果与结论:①3种模型在受不同侧向力的情况下,最大应力分布区域都集中在L_4皮质骨前部,而最大位移分布区域主要集中在L_5上;②不可代偿性模型(随访中发生不可代偿的躯干偏移)和可代偿性模型(随访中发生可代偿的躯干偏移)在受不同侧向力的情况下,应力分布几乎没有变化,但可代偿性模型在同样载荷作用下会产生更大的位移变化,而且刚度也明显小于不可代偿性模型,即可代偿模型在受到同等力的作用下更容易变形;③结果提示,通过三维有限元模型可以完成对先天性脊柱侧凸冠状面腰骶段柔韧性的生物力学分析,而且生物力学结果也与作者的临床设想一致,即可代偿性先天性脊柱侧凸患者腰骶段椎体间角度变化的幅度更大,提示其腰骶段柔韧性更好。

BACKGROUND： In the patients with congenital scoliosis, the spinal motor units exhibit developmental disorders and poor range of motion. It has been found that the compensation ability of coronal lumbosacral region （L4-S1） is associated with the occurrence of non-compensable trunk migration postoperatively.OBJECTIVE： To establish the three-dimensional finite element models of coronal lumbosacral region of normal and patients with congenital scoliosis and to compare the strain, displacement, stress and stiffness under different loading conditions among models.METHODS： One normal subject and two congenital scoliosis patients with different coronal lumbosacral region flexibility were selected, DICOM image datawere obtained by spiral CT scanning at the lumbosacral region, and then imported into MIMICS software, and a three-dimensional model was established according to the gray values of each tissue on CT,followed by simplified by GEOMAGIC, and finally imported into ABAQUS foftware to conduct a mechanic analysis under different loading conditions.RESULTS AND CONCLUSION： （1） Under different lateral forces, in the three models, the maximum stress mainly distributed on the frontal region of L4 cortical bone, and maximum displacement concentrated on L5. （2） There was no significant change in the stress distribution in the two scoliosis models, but the compensable model showed larger displacement change, and its stiffness was significantly less than that of the non-compensable model, indicating that the compensable model is easy to deform. （3） These findings suggest that three-dimensional finite element model is helpful to perform a biomechanical analysis for coronal lumbosacral region of congenital scoliosis, among which, a compensable model exhibits large displacement, suggesting a good flexibility.