腰椎间盘摘除三维有限元模型的生物力学分析

Biomechanical analysis of three-dimensional finite element models of lumber intervertebral disc removal

目的:建立腰椎运动节段椎间盘摘除的三维有限元模型,分析椎间盘摘除后腰椎生物力学的改变。方法:实验于2003-12/2004-08在中南大学湘雅医院骨科研究室完成。以1名健康男性志愿者作为模拟对象,对其脊柱T12～S1节段进行层厚2mm的连续扫描,共获得CT断层图像264幅,并对CT图像每隔15°进行三维重建。将CT扫描的腰椎图像结合人体解剖学数据通过3DSMAX软件建模形成正常中国男性L4～5运动节段的三维模型,用有限元分析软件转换成有限元模型。在此模型上去除L4～5椎间盘右后侧1/4的纤维环中部全层及约1/4的髓核,以模拟腰椎间盘摘除手术。分别在椎体、椎间盘及小关节选取节点进行计算。结果:①2000N垂直压缩载荷下椎间盘摘除后运动节段应力与正常运动节段的比较:与正常运动节段比较,垂直压缩时上下椎体、纤维环及髓核右后方压力均升高,其余部分压力降低;双侧小关节内压力升高(P均<0.01)。②10N·m前屈载荷下椎间盘摘除后运动节段应力与正常运动节段的比较:与正常运动节段比较,前屈时上下椎体、髓核左前方压力均升高;纤维环前方压力、后方张力均升高;双侧小关节内压力降低(P均<0.01)。③10N·m后伸载荷下椎间盘摘除后运动节段应力与正常运动节段的比较:与正常运动节段比较,后伸时上下椎体、纤维环前方张力、后方压力均升高;髓核前方压力降低,后方压力升高;双侧小关节内压力升高(P均<0.01)。④10N·m侧弯载荷下椎间盘摘除后运动节段应力与正常运动节段的比较:与正常运动节段比较,侧弯时上下椎体、纤维环、髓核右侧压力均升高,左侧压力降低;右侧小关节内压力升高,左侧小关节承受的张力改变为压力(P均<0.01)。结论:成功建立了L4～5腰椎运动节段椎间盘摘除的新型三维有限元模型,应力分析证实腰椎间盘摘除改变了腰椎运动节段正常的承载方式,小关节等部位存在较高的应力,提示这可能是术后邻近部位发生继发性退行性变的原因。

AIM： To establish the three-dimensional models of motor segment removals in the lumbar intervertebral disk, and analyze the biomechanical change after the removal. METHODS： The experiment was conducted at the Orthopaedics Laboratory, Xiangya Hospital of Center-South University between December 2003 and August 2004. One healthy man volunteered to be the model subject, whose spine T12-S1 segments were scanned continuously with the width of 2 mm. Totally 264 CT fault images were obtained, and given three-dimensional construction every 15°. The scanned CT images of lumbar vertebra were combined with human anatomy data to establish the three-dimensional models of L4-5 motor segments in normal Chinese men with 3DSMAX software, which was then transformed to finite element models with analysis software. The 1/4 fibrous ring in the right posterior of L4-5 intervertebral disc and 1/4 nucleus pulposus were wiped out from the finite element models so as to model the lumbar intervertebral removal operation. The segments selected respectively from vertebral body, intervertebral disc and tiny joint were counted. RESULTS： The stress in normal motor segment and motor segment after intervertebral disc removal were compared in the following conditions： ①In 2000N vertical compression： Compared with the normal motor segment, the pressures increased in the upper and lower vertebral bodies, fibrous rings and nucleus pulposus while decreased in other divisions; The intraarticular pressures （IAP） were also increased in bilateral tiny joint （P 〈 0.01）.②In 10 N .m antexion： Compared with the normal motor segment, the pressures enhanced in the upper and lower vertical bodies and nucleus puiposus; The front pressure and rear tension were enhanced in the fibrous rings; The IAP was decreased in the bilateral joint（P 〈 0.01）.③In 10 N .m back-extension： Compared with the normal motor segment, the pressures of upper and lower vertical bodies, the front tension and rear pressure of fibrous ring were all increased; The pressures increased in the front but decreased in rear of nucleus pulposus; The IAP also enhanced in the bilateral joint （P 〈 0.01）. ④In 10 N .m inclined bending： Compared with the normal motor segment, the pressures raised in the upper and lower vertical bodies, fibrous ring and right nucleus pulposus while decreased in the left nucleus pulposus; The right IAP enhanced and right tension were changed into pressure （P 〈 0.01）. CONCLUSION： The three-dimensional finite element models have been established successfully after L4-5 lumbar motor segment intervertebral disc were removed. The stress analysis confirms that, the lumbar intervertebral disc removal can change the normal bear-weight way of lumbar motor segment. The high IAP indicates that it may be the reason for secondary degeneration in the neighboring locus after operation.