伴椎动脉高跨的Ⅱ型齿状突骨折后路寰枢椎固定术的有限元分析

研究伴枢椎单侧椎动脉高跨的Ⅱ型齿状突骨折采用两种组合后路寰枢椎内固定术式治疗的生物力学特性,分析上颈椎的稳定性和内固定植入椎板螺钉、椎弓根螺钉和C2pars螺钉的应力分布情况。基于人体颈椎Ⅱ型齿状突骨折的CT图像数据,结合有限元前处理软件,依据临床手术方案,建立上颈椎两种组合后路寰枢椎内固定模型:一种是单侧枢椎椎板螺钉(C2TL)+寰枢椎椎弓根螺钉(C1PS、C2PS)固定(C1PS-C2TL+PS模型),另一种是单侧C2pars螺钉+寰枢椎椎弓根螺钉固定(C1PS-C2pars+PS模型),分析两种固定模型在屈伸、侧弯和旋转工况下的关节活动度和内固定植入器械的应力分布情况。结果表明,伴椎动脉高跨Ⅱ型齿状突骨折在后路寰枢椎两种固定术式中,C1PS-C2TL+PS模型在屈伸、侧弯和旋转工况下寰枢关节的关节活动度比骨折模型分别减小92.71%、91.28%、95.89%,C1PS-C2pars+PS模型分别减小89.50%、94.77%、92.72%,表明椎体固定节段的刚度都显著提高。此外,C1PS-C2pars+PS模型在前屈和后伸运动时,枢椎螺钉的根部和连接棒下部出现明显的应力集中,最大应力值分别为179.9和167.6MPa,比C1PS-C2TL+PS模型分别增大55.1和52.2MPa。C2pars螺钉在不同工况下最大应力值的变化幅度比较显著,最大值为前屈工况的123.7MPa,比C2TL最大应力值增大21.4MPa。伴椎动脉高跨的Ⅱ型齿状突骨折采用C1PS-C2TL+PS和C1PS-C2pars+PS两种固定术式,均能有效地提高寰枢椎的刚度,前者在屈伸和旋转时具有更好的稳定性,C1PS-C2TL+PS内固定术式在结构和应力分布上更加合理,结果可为伴椎动脉高跨Ⅱ型齿状突骨折内固定术式的研究提供一定的理论依据。

Finite Element Analysis of Posterior Atlantoaxial Fixationfor Type II Odontoid Process Fracture with High-Riding Vertebral Artery

To investigate the biomechanical characteristics on the treatment of type II odontoid process fracture with axial unilateral high-riding vertebral artery by two kinds of the combined posterior atlantoaxial fixation,the stability of the upper cervical vertebra and the stress distribution of the internal fixation implants translaminar screw,pedicle screws and C2 pars screw were analyzed. Based on the CT image data of type II odontoid process fracture of human cervical spine,combined with the finite element pre-processing software,according to the clinical operation plan,the posterior atlantoaxial fixation models of two combinations of upper cervical vertebra were established:1) unilateral axial translaminar screw + atlantoaxial pedicle screws fixation (C1PS-C2TL+PS);2) unilateral C2 pars screw + atlantoaxial pedicle screws fixation (C1PS-C2pars+PS). The range of motion and the stress distribution of internal fixation implants of two fixed models were analyzed under flexion and extension,lateral bending and rotation. In the two kinds of posterior atlantoaxial fixation on the treatment of type II odontoid process fracture with unilateral high-riding vertebral artery,the range of motion of the atlantoaxial joint of C1PS-C2TL+PS model decreased by 92.71%,91.28%,95.89% respectively under flexion and extension,lateral bending and rotation,and C1PS-C2pars+PS model decreased by 89.50%,94.77% and 92.72% respectively,all of which indicated that the stiffness of the fixed segments of vertebral body was significantly improved. In addition,the stress of C1PS-C2pars+PS model at the root of the axial screw and the lower part of the connecting rod was significantly concentrated under the flexion and extension conditions,with the maximum stress values of 179.9 and 167.6 MPa respectively,which was 55.1 and 52.2 MPa higher than those of C1PS- C2TL+PS model. The maximum stress values of C2pars screw under different conditions changed greatly,the maximum value was 123.7 MPa under flexion condition,which was 21.4 MPa higher than the maximum stress value of C2TL. In conclusion,the two fixed operations of C1PS-C2TL+PS and C1PS-C2pars+PS could effectively improve the stiffness of atlantoaxial for type II odontoid process fracture with high-riding vertebral artery,the former has better stability in flexion and extension and rotation,and the C1PS-C1TL+PS internal fixation is more reasonable in structure and stress distribution. These results provided theoretical basis for the study of internal fixation for type II odontoid process fracture with high-riding vertebral artery.