Modification and validation of Lenke3 type adult idiopathic scoliosis finite element model

doi:10.3969/j.issn.2095-4344.2017.31.010

Abstract

Abstract:

BACKGROUND: A Lenke3 type adult idiopathic scoliosis finite element model was established successfully using Mimics software. However, whether the model fits the actual conditions of individualized patients still requires a further revision and validation.

OBJECTIVE: To modify and validate the Lenke3 type adult idiopathic scoliosis finite element model by finite element analysis software.

METHODS: Based on the characteristics of Lenke3 adult idiopathic scoliosis model, the three-factor and three-level orthogonal experiment was used to optimize the finite element model, making it more close to the actual one. The vertebrae at T₁-T₄, T₅-T₈ and L₆-S₁ levels (sacral lumbarization) were loaded to simulate left and right lateral flexion, as well as extension and flexion, and the range of motion when left and right rotation were compared with Busscher and Yamamoto experiments in vitro.

RESULTS AND CONCLUSION: (1) According to the orthogonal experiment, the mean difference and range of each factor and each level were calculated, and finally A1B2C3 combination was the optimal one that can make the model largely consistent with the real situation. The difference in Cobb angles between the clinical lateral flexion test and the parameter pre-modified model simulation was 54.44°, which was decreased to 2.11° after modification. Moreover, the maximum difference in each scoliosis Cobb angle of the modified model was 4.29°. (2) The simulation results of the modified model when compared with the X-ray images when left and right lateral flexion, the two data obeyed normal distribution, so the paired t test was used: left lateral flexion, P =0.082 (P > 0.05); right lateral flexion, P=0.421 (P > 0.05); supine position, P=0.160 (P > 0.05). (3) The range of motion at T₁-T₄ segments was as followings: left flexion, 3.25°; right flexion, 3.32°; anteflexion 2.52°; extension, 2.89°; left rotation, 3.73°; right rotation 3.76°; the range of motion at T₅-T₈ segments: left flexion, 1.39°; right flexion, 1.43°; anteflexion 1.35°; extension, 1.34°; left rotation 2.09°; right rotation 2.11°; the range of motion at L₆/S₁: left flexion: 5.17°; right flexion: 5.19°; anteflexion: 8.92°; extension: 7.35°; left rotation: 1.41°; right rotation: 1.42°. The results were almost consistent with Busscher and Yamamoto experimental results. (4) To conclude, the model is in good agreement with the patient’s actual properties after modification. The modified model has good reliability and validity, and provides valid data platform for simulating clinical operation in the future.

中国组织工程研究杂志出版内容重点：人工关节；骨植入物；脊柱；骨折；内固定；数字化骨科；组织工程

Key words: Scoliosis, Finite Element Analysis, Tissue Engineering

CLC Number:

R318

Xin Da-qi, Hu Zhen-ming, Han Di, Yang Xue-jun, Xiao Yu-long, Xing Wen-hua, Zhao Yan, Fu Yu, Zhu Yong. Modification and validation of Lenke3 type adult idiopathic scoliosis finite element model[J]. Chinese Journal of Tissue Engineering Research, 2017, 21(31): 4975-4982.

Figures/Tables 4

2.1 模型的参数修正分析结果研究采用直观分析法对临床左右侧屈试验和模拟实验结果的差异进行分析，如表2所示。直观分析表的结果显示，各因素对模拟实验结果差异的影响大小顺序为B>C>A，即因素B影响最大，而因素A影响最小。对于实验选择的含有双弯畸形的Lenke3型成人特发性脊柱侧凸患者，此实验结果最符合患者临床真实情况。A1B2C3的最佳组合可使模拟实验结果最符合个体的真实情况，即上胸段、胸椎侧凸及腰椎侧凸的椎间盘材料属性系数分别为0.2，1和8时，使得有限元模拟实验结果与患者临床真实情况的差异最小化。根据临床和有限元模拟Cobb角的变化差异公式计算得出，临床侧屈实验和参数修正前模型模拟的Cobb角度的变化差异值为54.44°，经过参数修正后模型的差异值减小为2.11°，见表3。 2.2 模型的有效性验证结果 2.2.1 几何形态相似性验证结果参数修正后的成人特发性脊柱侧凸模型的几何外形基本符合仰卧位全长脊柱X射线片，如图3所示。其中，两者之间各侧凸Cobb角的最大差异为4.29°。 2.2.2 成人特发性脊柱侧凸仰卧位左右侧屈试验验证结果左侧屈位时，在T1椎体右侧面均匀加载的力的大小为65.9 N时，模型的T1椎体质心在X轴上向左移动的距离为-204.22 mm，与临床X射线片上实际偏移距-203.69 mm相差了0.53 mm；而右侧屈位时，在T1椎体左侧面均匀加载的力的大小为75.8 N时，模型T1椎体质心在X轴上向右移动的距离为178.79 mm，与临床X射线片上实际偏移距离179.26 mm相差了0.47 mm，两者其差值均小于实验设计规定的1 mm，故可以认为有限元模型模拟左右侧屈试验有效。优化模型模拟左右侧屈试验与仰卧位左右侧屈X射线片相比较，其各侧凸Cobb角度最大相差为4.29°，见表4。同样，将有限元模型与仰卧侧屈位X射线片T1-L6椎体质心至骶骨中垂线的偏离距离进行对比，见表5。参数修正后的成人特发性脊柱侧凸模型模拟侧屈试验图片上的每个椎体质心连线与仰卧左右侧屈位X射线片基本一致，见图4。经SPSS 20.0统计软件计算得出：2组配对数据均服从正态分布，故利用配对t 检验进行计算。左侧屈时，P=0.082， P > 0.05；右侧屈时，P=0.421(P > 0.05)，仰卧位P=0.160，P > 0.05，各组差异均无显著性意义，可认为X射线与优化后的2组数据之间差异无显著性意义。 2.2.3 分节段加载实验验证结果 T1-T4节段模型的验证结果：将T1-T4节段的有限元模型分别加载4 N•m力矩，分别模拟前屈、后伸、左右侧屈和左右旋转，划分体网格后的图片见图5，其载荷下的位移云图见(图6-8)。上胸段(T1-T4)的有限元模型分别加载4 N•m力矩的屈伸、左右侧屈和左右旋转载荷作用下，将T1-T4节段各个方向的ROM，分别为左侧屈3.25°，右屈3.32°，前屈2.52°，后屈2.89°，左侧旋转3.73°，右侧旋转3.76°，获得的结果与Busscher等[10]的实验结果进行比较，两者结果基本吻合，如图9所示。 T5-T8节段模型的验证结果：将T5-T8节段的划分体网格的有限元模型见图10，分别加载4 N•m力矩，分别模拟前屈、后伸、左右侧屈和左右旋转，其载荷下的位移云图见图11-13。左右旋转载荷作用下，将T5-T8节段各个方向的ROM结果左屈1.39°，右屈1.43°；前屈1.35°，后伸1.34°；左旋2.09°，右旋2.11°；获得的结果与Busscher等[10]的实验结果进行比较，两者结果基本吻合，如图14所示。 L6-S1节段(骶椎腰化)模型的验证结果：患者由于骶椎腰化，故模型模拟L6-S1节段的有限元模型与其他作者报道的L5-S1相似，模型L6-S1的网格化模型见图15，分别加载10 N•m力矩的屈伸、左右侧屈和左右旋转载荷下的位移云图见图16-18。腰骶段(L6-S1)的有限元模型分别加载10 N•m力矩的前屈、后伸，左右侧屈和左右旋转载荷下，获得L6/S1节段各个方向的ROM结果分别为左侧屈5.17°，右侧屈5.19°，前屈8.92°，后伸7.35°，左旋1.41°，右旋1.42°，与Yamamoto等[11]的实验结果进行对比分析，从数据分析可知：本实验提取节段的模型与Yamamoto等报道的实验结果基本吻合，结果如图19所示。本实验将建立好的原始模型通过侧弯的特点分为3个区域即上胸椎、胸椎侧弯、腰椎侧弯，同时将模型的3个区域的椎间盘材料属性分为3个水平，通过利用三因素三水平正交试验计算出各参数的最佳组合，实验组合为A1B2C3，椎间盘模型影响最大的为胸椎侧弯，这与志愿者X射线柔韧性分析相符合，通过对初始模型进行参数修正处理，使得模型与患者真实的材料属性基本符合。再将修正后的模型分别与临床仰卧位全脊柱X射线片、左右侧屈位X射线做对比，同时将T1-T4活动度、T5-T8活动度、L6/S1(骶椎腰化)活动度与其他作者生物力学实验数据相比较，结果显示经过修正后的成人特发性脊柱侧凸模型与患者临床X射线片高度一致。同时与其他作者正常节段分段加载试验的结果一致，修正后的模型具有较好的可靠性和有效性，为下一步的模拟临床手术操作模拟提供了有效的数据平台。 "

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