寰椎椎弓根螺钉与侧块螺钉有限元分析比较

A finite element analysis for comparison of atlas pedicle screw and lateral mass screw

[目的]应用有限元方法比较寰椎椎弓根螺钉(pedicle screws, PS)与侧块螺钉(lateral mass screws, LMS)的力学稳定性。[方法]依据一名正常男性寰椎CT扫描资料逆向重建寰椎三维模型,再以Hypermesh 12软件设置材料属性获得骨质疏松模型,最后运用Abaqus6.9软件分别测量寰椎PS与LMS在单皮质置钉和双皮质置钉情况下轴向拔出力与应力分布。[结果]骨质疏松和正常骨质状态下,PS组的单皮质骨和双皮质置钉的最大拔出力均大于LMS组,PS组双皮质置钉的最大拔出力大于单皮质置钉,而LMS组双皮质置钉的最大拔出力大于单皮质置钉。PS和LMS组双皮质置钉和单皮质置钉的最大拔出力在骨质正常状态下均大于骨质疏松状态。单皮质PS应力分布在钉体的近端和中段,其中进钉点附近应力最大;双皮质PS应力分布在整个螺钉,以中段至近端应力较大,且越靠近尾端应力越大。[结论] PS钉道长、应力分布均匀,抗拔出强度显著优于LMS。

[Objective] To compare the mechanical stability of atlas pedicle screws(PS) versus lateral mass screws(LMS) by using finite element method. [Methods] Based on the CT scan data of a normal male atlas, the 3 D model of the atlas was reconstructed by reverse technique, and then the material properties were set with Hypermesh 12 to obtain the normal and osteoporosis models. Finally, Abaqus 6.9 software was used to measure maximal axial pullout force and stress distribution of the atlas PS and LMS placed through single-cortex and double cortex respectively. [Results] Under osteoporotic and normal bone conditions, the maximum pullout forces of PS group in both the single-cortical and double-cortical placements were greater than those of the LMS group. The double-cortical screw placement got greater maximum pullout force than single-cortical screw placement in both PS and LMS groups. In both the PS group and the LMS group under double-cortical and single-cortical screw placement, the maximum pull-out forces in normal bone state were greater than those in osteoporotic state. The stress was distributed in the proximal and mid-section of the screw body, and was the largest near the screw entry point in the single-cortical PS, whereas distributed throughout the screw, and was greater in the middle to the proximal end, greater as close to the end in the double-cortical PS. [Conclusion] The PS, with a long screw path and uniform stress distribution on it, has pull-out strength considerably superior to that of LMS.