寰椎三维有限元模型的建立及其骨折机制

Establishment of three-dimensional finite element model for ascertainment of atlas fracture mechanism

目的 建立寰椎的三维有限元模型 (FEM) ,并对寰椎各型骨折的可能机制予以分析。 方法 通过CT扫描获取寰椎的空间结构信息 ,利用软件建立其三维有限元模型 ,模拟临床的不同情况 ,以Ansys软件分析头颅位于屈曲位、后伸位以及头颅过度后伸时寰椎后弓与枢椎棘突接触等条件下 ,寰椎不同部位的应力变化情况。 结果 (1)在不同的边界条件下 ,头颅位于屈曲位或后伸位上关节面受来自头颅的纵向作用力时 ,应力最大点集中于前弓 ,次级应力集中区域为侧块及后弓。由于此时侧块上下方向的活动被限制 ,应力的集中是因上关节面受力后推压侧块向外侧滑移 ,使得前后弓受牵拉张力所致。 (2 )头颅过度后伸寰椎后弓与枢椎棘突接触时 ,后弓加载 ,应力明显集中于寰椎后弓的近侧块处。 结论 (1)无论头颅位于屈曲位、中立位或后伸位 ,当受纵向作用力时 ,首先引起的是寰椎前弓的骨折 ;如外力足够大或持续的时间较长 ,将导致Jefferson骨折产生。 (2 )单纯后弓骨折是由于头部后伸 ,在上关节面受轴向压力同时 ,寰椎后弓受到枕骨或枢椎棘突的作用 。

Objective To set up a three dimensional atlas finite element model (FEM) and evaluate the possible mechanism of various atlas fractures. Methods One intact fresh adult cadaveric atlas was scanned by CT with 1 mm interval. Then, the data of CT were utilized to establish the three dimensional FEM by using software PRO/E and simulate the different clinical conditions. Relying on the software Ansys, the changes of theoretical stress in different position of atlas were analyzed when the skull was in flexion and posterior extension, and when atlas posterior arch contacted with axis spinous process due to over posterior extension of the head. Results (1) No matter what positions the loading was placed on, the largest stress focused on the anterior arch, and next on the lateral mass and the groove of posterior arch when the superior joint surface was affected by axial stress and when the head was in positions of flexion or back extension. At the time, the upward and downward mobility of the lateral mass was inhibited because the stress concentration was caused by superior joint surface pressing lateral mass that made contraction and stress concentrate on the anterio posterior arch. (2) When the posterior arch contacted with the C 2 spinous, the largest stress significantly focused on the lateral mass of the posterior arch of the atlas. Conclusions (1) The axial loading will cause the anterior arch fracture first no matter what position including flexion, median position or posterior extension of the head is. Enough loading or over long time of loading will beget the Jefferson's fracture. (2) The causes for single posterior arch fractures include back extension of head, axial compression on superior joint, atlas posterior arch being pushed upward by occipital bone or C 2 spinous and the stress concentrating on the Achille's heel of atlas posterior arch.