应用C2～T1有限元模型研究椎体骨隧道技术对C4椎体上终板的生物力学影响

Evaluation of biomechanical changes on upper endplate with C4 transcorporeal tunnel using a C2～T1 finite element model

目的:研究经皮内镜下前路经椎体打孔颈椎间盘髓核摘除术(anterior transcorporeal approach of percutaneous endoscopic cervical discectomy,ATPECD)不同角度、直径的椎体骨隧道对C4椎体上终板的生物力学影响。方法:采集1位健康男性志愿者的颈部CT图像,建立C2～T1三维有限元模型。验证模型的有效性后,选择C4椎体按破坏和不破坏终板2种方式和不同打孔直径建立AB 2组模型(A6、A8、A10和B6、B8、B10)。对各模型施加1 N/m扭矩模拟颈椎屈曲运动,分析不同打孔方式和不同打孔直径对C4椎体上终板的生物力学影响。结果:(1)云图显示A组椎体上终板开口边缘均存在不同程度的应力集中,B组B10模型终板前份出现少量应力集中,其余模型无明显应力集中。2组模型上终板的应力集中范围和应力最大值均随钻孔直径增加而增加。2组模型C4上终板应力最大值分别为A6:11.51 MPa、A8:17.33 MPa、A10:18.49 MPa和B6:2.57 MPa、B8:2.89MPa、B10:3.65 MPa。(2)分析2种打孔方式在颈椎屈曲载荷下终板前后份的Mises应力分布。B6模型C4上终板前后份应力与正常模型相比无明显差异(P>0.05),B8模型C4上终板前份Mises应力与正常模型相比无明显差异(P>0.05),其他模型与正常模型存在明显差异(P=0.000)。(3)对各模型C4上终板进行骨折风险预测,结果提示A组模型上终板均存在不同数量的骨折高风险单元(A6:0.8%;A8:2.3%;A10:7.2%),而B组模型上终板骨折风险较低。结论:ATPECD手术所建立的2种类型的骨隧道中,破坏上终板的骨隧道会导致终板开口边缘应力集中及终板骨折风险,而不破坏终板的骨隧道可以避免上述风险。为了将终板骨折风险控制在较低范围内,不破坏终板的骨隧道应控制直径在椎体前缘高度的2/3以内,破坏终板的骨隧道应控制直径在椎体前缘高度的1/2以内,并且应避免破坏终板中心区域。

Objective：To evaluate the biomechanical changes on C4 superior endplate with different types and diameters of transcorpo-real tunnels. Methods：A C2-T1 finite element model was built with CT data of neck from a healthy male volunteer. After validation of the FE model,two groups（A and B） of C2-T1 models was built with C4 tunneled with or without endplate excision and diameters of 6 mm,8 mm and 10 mm（1/2,2/3 and 6/5 of anterior C4 vertebral body height）. 1 N/m of flexible moment was loaded to FE models and the biomechanical changes on C4 superior endplate was evaluated. Results：There were stress concentration on the margin of ex-cision on C4 superior endplates in group A;in group B only B10 showed stress concentration on C4 superior endplate. All the areas and values of stress concentration increased with diameter in two groups. Maximum stress on C4 superior endplates in two groups was A6：11.51 MPa,A8：17.33 MPa,A10：18.49 MPa and B6：2.57 MPa,B8：2.89 MPa,B10：3.65 MPa. One-way analysis of variance of the stress distribution of C4 on superior endplate between tunneled model and intact model showed that B6 and anterior of B8 end-plates had no significant difference with the intact model（P〉0.05）,while in other models the differences were significant（P=0.000）. Evaluation of the risk of fracture on endplates showed that there were different amounts of high risk elements（A6：0.8%;A8：2.3%;A10：7.2%） in group A while few risk elements in group B. Conclusion：Those tunnels on vertebrae with endplate excision would cause stress concentration and risks of end-plate fracture. Maintaining the integrity of superior endplate can avoid those risks. In order to avoid risks of endplate fracture,diameter of tunnels on vertebrae without endplate excision should be limited within 2/3 of anterior vertebral body height,diameter of tunnels on vertebrae with endplate excision should be limited within 1/2 of anterior vertebral body height.