人工寰齿关节置换后寰枢椎骨性结构生物力学性能的有限元分析

Finite element analysis of biomechanical performance of atlanto-axial bony structure following artificial atlanto-odontoid joint arthroplasty

目的利用三维有限元分析研究人工寰齿关节固定模型在不同工况下寰枢椎骨性结构的应力特点，并从应力角度探讨改良人工寰齿关节的方向。方法通过CT扫描获取人工寰齿关节和颈椎图像信息，应用Mimics软件、Freeform软件和Ansys软件建立人工寰齿关节固定的三维有限元模型，观察前屈、后伸、侧弯、旋转载荷下固定整体的应力特点，分析人工寰齿关节固定模型中骨性结构的生物力学特性。结果在前屈状态下，寰椎侧块与后弓交界处最大应力值为0．138×10^8N／m^2，枢椎钉孔处、钢板与枢椎接触处和枢椎椎弓处最大应力值为0．201×10^8N／m^2。在后伸运动状态下，寰椎侧块与椎弓根交界处最高应力值为0．666×10^7N／m^2，枢椎椎弓处应力最高应力值为0．254×10^8N／m^2。寰枢椎钉孔处出现应力集中。在右侧弯状态下，寰椎右侧块钉孔处最高应力值为0．124×10^8N／m^2，枢椎与钢板右侧接触处最大应力值为0．178×10^8N／m^2。在右旋转状态下，寰椎两侧后弓与侧块交界处最大应力值为0．847×10^7N／m^2，枢椎与钢板接触处最大应力值为0．170×10^9N／m^2。所建立的有限元模型较好地描绘了人工寰齿关节固定的结构特点，共包含28620个结点、107441个单元。在不同的工况下，应力主要分布在金属与椎体接触处、钉孔处、寰椎侧块一后弓交界处和枢椎椎弓根处。结论人工寰齿关节置换后寰枢椎应力分布较其完整状态时发生改变，对应力有一定的分载作用。利用有限元法可以较完整分析人工寰齿关节固定模型的受力情况。

Objective To investigate the stress characteristics of atlanto-axial bony structure under conditions of anteflexion, posterior extension, lateral flexion, and rotation after artificial atlanto-odontold joinarthroplasty using three-dimensional finite element method and to improve the orientation of artificial atlantoodontoid joint from perspective of stress. Methods A three-dimensional finite element model of prosthetic atlanto-odontoid joint arthroplasty was created from CT images of the artificial atlantoodontoid joint and cervical vertebrae using software Mimics, Freeform, and Ansys. Stress characteristics of the model dealt with proneness, posterior extension, lateral flexion, or rotation loads were observed. Biomechanical performance of the bony structure of the model was analyzed and the orientation in improving the prosthesis was discussed. Results Anteflexion loading produced a maximum stress of 0. 138× l0^8 N/m^2 at the junction of lateral mass and posterior arch of the atlas, and 0. 201 × 10^8 N/m^2 at axial nail hole, contact point of plates with the axis, and posterior arch of the axis. Posterior extension loadingproduced a maximum stress of 0. 666 × 10^7 N/m^2 at junction of lateral mass and posterior arch of the atlas and 0.254 × 10^8 N/m^2 at arch of the axis. Besides, stress concentration occurred at atlantoaxis nail hole. Right bending produced a maximum stress of 0. 124 × l0^8 N/m^2 at nail hole of right mass of atlas and 0. 178 × l0^8 N/m^2 at right contact point of the axis with plates. Right rotation produced a maximum stress of 0. 847 ~ 107 N/m2 at junction of lateral mass and posterior arch of the atlas and 0. 170 × 10^9 N/m^2 at contact point of the axis with plates. ＇The finite element model comprised 28 620 nodes and 107 441 units and provided good defining of the structural properties of artificial atlanto-odontoid joint arthroplasty. Un- der different loading conditions, the stress was mainly distributed in contact point of the vertebral body with plates, nail holes, junction of lateral mass and posterior arch of the atlas, and axial pedicle. Conclusions Prosthetic atlanto-odontoid joint scatters a part of the stress and alters the stress distribution of the atlas and axis from the intact condition. Finite element method can obtain complete analysis of the stress distribution of the artificial atlanto-odontoid joint arthroplasty.