腰椎间孔成形幅度对腰椎生物力学影响的三维有限元分析

Lumbar biomechanical characteristics after foraminoplasty in different amplitudes: a finite element analysis

目的应用腰椎L_(3~5)节段三维有限元模型,分析椎间盘摘除+不同幅度椎间孔成形前后对腰椎生物力学的影响。方法选取1位20岁既往无腰椎疾病史中国男性志愿者的CT数据,在Mimics 15.0软件中建立L_(3~5)节段三维有限元模型,在Geomagic 12.0中修补、降噪及曲面化,在Pro/E 5.0中行椎间盘的曲面建模,修改髓核和纤维环的材料参数模拟L_(4~5)椎间盘中度退变(模型M1),在Hypermesh 12.0中进行有限元网格处理,并导入ABAQUS软件进行分析。模拟经皮椎间孔脊柱内镜技术侧后入路,以上关节突尖部到下位椎体后上缘中点为穿刺基线建立通道,去除椎间盘左后侧约1/4的纤维环中部及1/4的髓核,以模拟腰椎间盘摘除手术,构建模型M2,以圆柱体代替环锯模拟切除上关节突部分骨质行椎间孔扩大成形术,构建一级椎间孔成形模型M3(环锯直径5mm)、二级椎间孔成形模型M4(环锯直径6.5mm)和三级椎间孔成形模型M5(环锯直径7.5mm),给予特定加载条件,比较其在前屈、后伸、左右侧弯、左右旋转6种工况下的生物力学特征。结果建立了有效的L_(3~5)三维有限元模型,除了在后伸工况下L_4椎体的位移无明显变化外,其他5种工况下椎间孔成形后L_4椎体的位移均有所增加,但成形的幅度对L_4椎体的位移无明显影响。M1模型在各种工况下L_(4~5)关节突关节的应力左侧较右侧大。M2模型在腰椎前屈及右旋工况下L_(4~5)左侧关节突关节的应力下降,右侧的应力上升;腰椎后伸下L_(4~5)左侧关节突关节的应力上升,右侧的应力下降;腰椎左侧屈工况下L_(4~5)关节突关节的左右两侧应力均上升;腰椎右侧屈工况下L_(4~5)关节突关节的左右两侧应力均下降。除腰椎左旋工况下M5模型的L_(4~5)右侧关节突关节应力增加明显外,其他各种工况下M3、M4、M5模型L_(4~5)关节突关节应力变化不明显。结论在精确穿刺的指引下,1~3级椎间孔成形对术后即刻的腰椎稳定及关节突关节的应力分布无明显影响。

Objective To analyze lumbar biomechanical characteristics after foraminoplasty in different amplitudes based on a three-dimensional finite element model of L3-5 segments of the lumbar spine. Methods A 20-year-old Chinese male volunteer who had no history of lumbar disease was selected. Using the obtained CT data, the three-dimensional model of L3-5 segment was established by Mimics15.0 software, and curved, repaired and denoised by Geomagic 12.0 software, the degeneration of L4-5（model M1） was simulated by modifying the material parameters of the nucleus pulposus and annulus fibrosus of intervertebral disc and grided by Hypermesh 12, and then was analyzed by ABAQUS software. The lumbar discectomy was simulated via percutaneous transforaminal endoscopic posterior approach to establish a channel between the midpoint of the tip of the protruding points and the top of the vertebral body, which removed the superior facet bone for foraminal ptasty, the whole layer of middle of the fiber ring at the 1/4 right of the inter-vertebral and about a quarter of the nucleus pulposus to establish model M2. The model of the first-stage foraminoplasty （model M3, diameter 5mm）, the second-stage foraminoplasty （model M4, diameter 6.5mm） and three-stage foraminoplasty （model M5, diameter 7.5ram） were established by using the cylinder instead of the trepan remove the superior facet bone for foraminoplasty. Under specific loading conditions, biomechanical characteristics of 6 kinds of loads （the forward bends, stretch, left and right side bend, rotate） were compared. Results An effective L3-5 three-dimensional finite element model was established. In addition to the displacement of the L4 vertebral body during extension, the forming of the lumbar intervertebral hole had no significant difference on the displacement of intervertebral lumbar.Different forming amplitude of intervertebral lumbar had no significant difference on the stress of the protruding joints. In the M1 model, the stress of the L4~~ left facet joints was larger than the right side under various conditions. In the M2 model, the stress L4_s left facet joints decreased in lumbar flexion and dextral, the stress increased on the right side. The stress on the right side of L4~5 facet joints increased in left lumbar flexion, but decreased on the right lumbar flexion. In addition to the stress of the L4~5 right facet joint increased significantly, and the stress changes of L4~~ facet joints of M3, M4, M5 models were not significant under other working conditions. Conclusion Under the guidance of the precise puncture, the hole forming of grade 1 to grade 3 lumbar in- tervertebral hole has no significant effect on the stabilization of the lumbar and the stress distribution of the joints.