不对称性Hangman骨折发生机制的有限元模型研究

目的 建立精细枢椎三维有限元模型,探讨不同约束条件下枢椎损伤机制和骨折类型. 方法 采集一名正常成年男性颈椎薄层CT数据集,在微机上基于CT数据利用Mimics10.01软件重建枢椎皮质骨和松质骨三维模型,再导入Ansys5.7有限元分析软件对模型赋予材料物理属性,模拟枢椎伤前不同位置下的受力条件.在齿突寰齿关节面上施加前后方向载荷,分析枢椎在三种不同约束条件下的应力、应变分布,及相对应条件下枢椎可能发生骨折的类型. 结果 当枢椎遭受前后方向剪切暴力:①双侧椎小关节约束模拟伤前枢椎于中立位,应力集中区对称位于枢椎关节突间部;②单侧椎小关节约束模拟伤前枢椎侧屈状态,最大应力集中位于约束侧关节突间部,高应力集中带经过椎体后角延伸进入椎体,对侧椎板与下关节突交界移行部位也出现应力集中;③椎体下方以及双侧小关节面约束模拟以往生物力学实验枢椎下方完全固定状态,高应力集中带位于齿状突与枢椎结合部位. 结论 伤前颈椎侧屈状态可能是导致不对称性Hangman骨折的一个非常重要因素;枢椎骨折的生物力学研究实验中,除加载暴力的方向外,标本不同约束固定方式直接影响枢椎骨折类型的复制.

Finite-element model analysis of asymmetrical Hangman's fractures

Objective To explore the injury mechanism and classification of axis fractures under different boundary conditions using precise 3D finite element models of axis. Methods Lamellar cervical CT data of a healthy adult man were collected and transferred into computer. Three-dimensional finite element models of cortical and trabecular bones of the axis were constructed from the CT data using MIMICS 10. 01software. Ansys 5.7 software was imported for material assignment and model analysis to simulate the axis injury situations. Theoretical stress distributions at the axis were calculated by applying anterior-posterior shearing force on the anterior articular surface of dens under 3 boundary conditions. The possible types of fracture that might occur under the corresponding conditions were explored. Results When the axis was subjected to anterior-posterior shearing force, 1 ) high stress concentrated at the bilateral pars interarticularis bilateral after inferior articular facet nodes of the axis were completely constrained to simulate the axis in neutral position before trauma; 2) high stress mainly distributed at one side of the pars interarticularis, the junction site of the inferior facet and laminae of the axis after one inferior articular facet node was completely constrained to simulate the axis lateral bending before trauma; 3) high stress concentration was located at the junction of the dens and axis after the inferior aspect nodes of the axis were completely constrained as in previous biomechanical studies. Conclusions Lateral bending of the cervical spine before trauma may be a very important factor to induce an asymmetrical Hangman's fracture. Besides the direction of violence, dif-ferent restrictions of the cadaverie sample might directly impact the reproduction of the axis fracture types in biomechanical studies of axis fractures.