前后路内固定治疗Ⅱ型不稳定Hangman骨折的有限元分析

目的 应用有限元方法分析评价前路钛板内固定和后路钉棒系统内固定两种术式治疗Ⅱ型不稳定Hangman骨折的生物力学差异。方法 建立完整上颈椎（C0~3）有限元模型并进行有效性验证。在此基础上建立失稳模型，并在失稳模型上分别建立装配前路钛板（titanium plate）和Cage植骨内固定模型（Plate+Cage模型）、后路C2椎弓根螺钉（C2 pedicle screws, C2PS）和C3侧块螺钉（C3 lateral mass screws, C3LMS）组成的钉棒系统内固定模型（C2PS+C3LMS模型）。在枕骨髁上施加40 N轴向压力模拟头颅重力，同时在枕骨上施加1.5 N?m力矩使模型产生前屈、后伸、侧弯、旋转运动，计算分析C2~3活动度（range of motion, ROM）、力的传导路径以及骨折线处的应变。结果 Plate+Cage模型在前屈、后伸、侧屈（单侧）和旋转（单侧）方向上C2~3的ROM比失稳模型分别减少了92.4%、97.1%、96.5%、90.0%，C2PS+C3LMS模型在各方向上比失稳模型分别减少了88.6%、90.2%、95.7%、90.3%。Plate+Cage模型在任何工况下的应力峰值均小于C2PS+C3LMS模型。结论 前路Plate+Cage内固定在前屈和后伸工况下比后路C2PS+C3LMS内固定具有更好的稳定性，而在侧屈和旋转工况下两者稳定性相当。前路Plate+Cage内固定在结构和应力分布上更加合理，可以实现复位、减压、固定、融合一步完成，是治疗Ⅱ型Hangman骨折的有效方法。
Objective To evaluate biomechanical differences between anterior titanium plate internal fixation and posterior pedicle screw internal fixation for treating type Ⅱ unstable Hangman’s fracture by finite element analysis. Methods An intact finite element model of the upper cervical spine (C0-3) was established and validated, and an unstable model was also established. Two different internal fixation models, i.e. anterior titanium plate+Cage with bone graft (Plate+Cage) and C2 pedicle screws+C3 lateral mass screws (C2PS+C3LMS) were established, respectively, based on the unstable model. The vertical load of 40 N was applied on the occiput to simulate head weight and 1.5 N?m torque was applied on the occiput to simulate loading conditions of flexion, extension, lateral bending and rotation. Range of motion (ROM) of C2-3, force pathway and strain at the fractured line were calculated and analyzed. ResultsCompared with the unstable model, the Plate+Cage model could decrease the ROM by 92.4%, 97.1%, 96.5% and 90.0%, while the C2PS+C3LMS model could decrease the ROM by 88.6%, 90.2%, 95.7% and 90.3%, in flexion, extension, lateral bending and axial rotation, respectively. The maximum stress of the Plate+Cage model was smaller than that of the C2PS+C3LMS model under 4 loading conditions. Conclusions The anterior Plate+Cage fixation possesses better stability than the posterior C2PS+C3LMS fixation in flexion and extension, while both fixation methods show similar stability in lateral bending and axial rotation. The anterior Plate+Cage fixation is more reasonable in structure and stress distributions, and can achieve reduction, decompression, fixation and fusion in one step, thus it is an effective operative procedure for treating typeⅡ Hangman’s fracture.