下颈椎全椎板切除后不同内固定技术螺钉的应力分布

Screw stress distribution of different fixation techniques following cervical laminectomy in lower cervical spine

目的：探讨下颈椎全椎板切除后不同内固定技术螺钉的应力分布规律。方法：采集1例成年健康男性志愿者下颈椎（C3~C7）的CT数据集,应用Mimics 10.01、Geomagic studio 10.0、Hyper Mesh 10.0、Abaqus 6.9.1等软件建立下颈椎（C3~C7）完整模型、三节段全椎板切除后模型、全椎板切除后椎弓根螺钉内固定（pedicle screw fixation,PSF）技术重建模型和经关节突螺钉内固定（transarticular screw fixation,TSF）技术重建模型。模拟施加75N头颅预载荷和1.0Nm运动附加力,使模型产生前屈、后伸、侧屈和旋转运动,分析两种内固定技术的螺钉应力分布情况。结果：所建完整下颈椎有限元模型与实体模型具有较好的几何相似性,共有61464个单元,16588个节点;加载后在各种工况下节间运动范围与文献实体测量结果吻合,表明完整模型有效。在此模型上建立了下颈椎三节段全椎板切除、PSF和TSF内固定重建的有限元模型。在各种工况下,PSF重建模型在钛棒与螺钉接合部易发生应力集中,应力峰值低于160MPa;TSF重建模型螺钉中部易发生应力集中,应力峰值高于2800MPa。结论：应用CT扫描数据建立的下颈椎三维有限元模型能模拟正常状态、全椎板切除及不同内固定技术重建,相比PSF重建技术,TSF有较高的断钉风险。

Objective：To investigate the screw stress distribution of different fixation techniques following cer- vical laminectomy in lower cervical spine.Method：CT scans were performed on a healthy adult male volun- teer.Mimics 10.01,Geomagic studio 10.0,HyperMesh 10.0 and Abaqus 6.9.1 softwares were used to establish the intact model （C3-C7）.The model was subjected to three-level laminectomy and then reconstructed by different fixation protocols：pedicle screw fixation（PSF） and transarticular screw fixation（TSF）.The skull load of 75N and torsion preload of 1.0Nm was added on the models,which simulate flexion,extension,lateral bending and rotation.The stress distribution were analyzed while the skull was under flexion,extension,lateral bending and rotation conditions.Result：The intact finite element model showed good geometric similarity,which consisted of 61464 elements and 16588 nodes.Compared with the published data,the intact model was validated.Base on the intact model,the models following laminectomy and then reconstructed either by PSF or TSF were es- tablished.Under simulated physiological movements,the screw inserted by PSF had higher stress bearing at the connection between screw and rod with the maximal stress levels of less than 160MPa,while screws inserted by TSF had higher stress bearing at the middle part with the maximal stress levels of over 2800MPa.Conclusion：Base on the CT scans,finite element model of lower cervical spine can simulate the conditions of natural state,after laminectomy and after reconstruction breakage under different fixation techniques.Compared with PSF techniques,TSF has a higher risk of screw.