计算机辅助改良椎板钩的设计及其固定腰椎峡部裂的生物力学有限元分析

Computer‑aided design of an improved lamina hook and finite element analysis of its use in fixation of lumbar spondylolysis

目的设计改良椎板钩系统,并与传统椎板钩系统固定腰椎峡部裂的生物力学特性进行比较。方法收集2021年1月至2022年8月中国人民解放军联勤保障部队第九四〇医院门诊体检的20名男性健康青年军人腰骶椎薄层CT数据。受试者年龄20~30岁[(25.0±3.0)岁]。通过三维建模软件,建立L_(5)椎体三维模型,测量L_(5)双侧椎板中间区域厚度、纵向最长径、下缘弧度半径、上下面尾端之间的夹角、下缘厚度及下缘最长径,进而设计新型改良椎板钩。再选择1名上述受试者,利用三维虚拟软件建立L_(4)~S节段线性有限元模型(正常模型,A模型),并在此基础上构建L_(5)双侧峡部裂模型(B模型)、改良与传统椎板钩固定模型(C、D模型)。通过约束骶骨两边,于L_(4)椎体上施加400 N纵向载荷模拟身体上1/3重力及沿X、Y、Z 3个方向上10 N·m的弯矩模拟前屈、后伸、侧弯及旋转等状态,评估A模型L_(4/5)节段和L_(5)/S_(1)节段活动度,并与既往研究进行对比,验证A模型的有效性;比较A、B、C、D模型的整体活动度、L_(4/5)和L_(5)/S_(1)节段活动度、整体最大位移、峡部的最大位移与最大应力,C、D模型中内固定的应力分布和最大应力,以及C、D模型中椎体的应力分布和最大应力。结果(1)A模型L_(4/5)节段在前屈、后伸、侧弯、旋转时的活动度分别为5.01°、4.03°、3.91°、1.42°,L_(5)/S_(1)节段活动度分别为4.62°、2.51°、2.40°、1.23°。(2)A、C、D模型的整体活动度、L_(4/5)和L_(5)/S_(1)节段活动度、整体最大位移在轴向压缩、前屈、后伸、左侧弯及左旋转时结果相似,而B模型则明显增大。(3)A、C、D模型在不同运动状态下峡部的最大位移差异不明显,而B模型峡部的最大位移均明显高于A、C、D模型,尤其在旋转时更明显,较A、C、D模型分别增大295%、277%、276%。C模型峡部的最大应力分别为0.938 MPa、1.698 MPa、0.410 MPa、2.775 MPa、1.554 MPa,D模型峡部最大应力分别为0.590 MPa、1.297 MPa、0.520 MPa、3.088 MPa、2.072 MPa,C、D模型在轴向压缩、前屈时峡部最大应力相似,但C模型在后伸、侧弯、旋转时峡部应力均小于D模型,C模型较D模型分别减小21.1%、10.2%、25.0%。(4)C模型在前屈、后伸、左侧弯、左旋转时内固定最大应力分别为135.220 MPa、130.180 MPa、200.940 MPa、306.340 MPa,D模型分别为131.840 MPa、112.280 MPa、349.980 MPa、370.140 MPa,2种模型在前屈、后伸时内固定的最大应力变化相当,但在左侧弯及左侧旋转时C模型较D模型减小42.6%、17.2%。(5)C模型在前屈、后伸、左侧弯、左旋转时椎体的最大应力分别为79.787 MPa、36.857 MPa、37.943 MPa、96.965 MPa,D模型椎体的最大应力分别为80.104 MPa、64.236 MPa、196.010 MPa、193.020 MPa,且2种模型最大应力均分布在与内固定接触区域,尤其在后伸、左侧弯、左旋转时C模型较D模型分别减少42.6%、80.6%、49.8%。结论改良椎板钩更符合国人椎板解剖结构。与传统椎板钩系统相比,改良椎板钩系统能有效降低腰椎峡部裂在各方向的位移及活动度,使内固定及椎体的应力明显减小,具有更好的生物力学性能。

Objective To design an improved lamina hook system and compare its biomechanical properties with traditional lamina hook system in fixation of lumbar spondylolysis.Methods The thin layer CT data of the lumbosacral vertebrae of 20 healthy young male servicemen who underwent physical examination in the outpatient department of the 940th Hospital of Joint Logistics Support Force of PLA from January 2021 to August 2022 were collected.The age of the subjects was 20-30 years[(25.0±3.0)years].A 3‐dimensional model of the L_(5)vertebral body was constructed using the 3‐dimensional modeling software.The new improved lamina hook was designed according to the measurements including the thickness of the middle area,the longest longitudinal diameter,the curvature radius of the lower edge,the angle between the upper and lower tail ends,the thickness of the lower edge,and the longest diameter of the lower edge of the bilateral L_(5)vertebral plates.One serviceman was selected from the aforementioned group to construct a linear finite element model of segments L_(4)‐S using the 3‐dimensional virtual software(normal model,model A),based on which,the L_(5)bilateral spondylolysis model(model B),improved lamina hook model(model C)and traditional lamina hook models(model D)were designed.By constraining both sides of the sacrum and applying a longitudinal load of 400 N on the L_(4)vertebral body,the upper 1/3 gravity of the body was simulated,and with a bending moment of 10 N·m along the X,Y,and Z directions,motions of forward flexion,backward extension,lateral bending,rotation,etc were simulated.The range of motion of segment L_(4/5)and L_(5)/S_(1)of model A was evaluated and compared with the findings of the previous researches to verify its effectiveness.The overall range of motion of models A,B,C,and D,the range of motion of segment L_(4/5)and L_(5)/S_(1),the maximum overall displacement,the maximum displacement and stress of the isthmus,the stress distribution and maximum stress of internal fixation of models C and D,and the stress distribution and maximum stress of the vertebral body of models C and D were compared.Results(1)During forward flexion,backward extension,lateral bending and rotation,the range of motion of model A was 5.01°,4.03°,3.91°and 1.42°in segment L_(4/5),and was 4.62°,2.51°,2.40°and 1.23°in segment L_(5)/S_(1).(2)The overall range of motion,range of motion of segment L_(4/5)and L_(5)/S_(1)and maximum overall displacement of models A,C,and D were similar in axial compression,forward flexion,backward extension,left bending,and left rotation,while those of model B were significantly increased.(3)There was no significant difference in the maximum displacement of the isthmus of models A,C,and D under different motion modes,while the maximum displacement of model B in the isthmus was significantly larger than that of models A,C,and D,especially during rotation,increased by 295%,277%,and 276%respectively.The maximum stress of the isthmus of model C was 0.938 MPa,1.698 MPa,0.410 MPa,2.775 MPa,and 1.554 MPa respectively.The maximum stress in the isthmus of model D was 0.590 MPa,1.297 MPa,0.520 MPa,3.088 MPa,and 2.072 MPa respectively.The maximum stress of the isthmus of models C and D was similar during axial compression and forward flexion,while the stress of the isthmus of model C was smaller than that of model D during backward extension,lateral bending,and rotation,decreased by 21.1%,10.2%,and 25.0%respectively compared with model D.(4)The maximum stress of internal fixation in models C and D during forward flexion,backward extension,left bending,and left rotation was 135.220 MPa,130.180 MPa,200.940 MPa and 306.340 MPa respectively,and was 131.840 MPa,112.280 MPa,349.980 MPa and 370.140 MPa respectively.The maximum stress of internal fixation in the two models of internal fixation during forward flexion and backward extension was similar,while it was decreased by 42.6%and 17.2%in model C during left bending and left rotation,compared with model D.(5)The maximum stress of the vertebral body during forward flexion,backward extension,left bending,and left rotation was 79.787 MPa,36.857 MPa,37.943 MPa and 96.965 MPa respectively in model C,but was 80.104 MPa,64.236 MPa,196.010 MPa and 193.020 MPa respectively in model D.The maximum stress of models C and D was all distributed in the contact area with the internal fixation,and especially during backward extension,left bending,and left rotation,when it was reduced by 42.6%,80.6%,and 49.8%of model C respectively,compared with that of model D.Conclusions The improved laminar hook is more consistent with the Chinese anatomized structure of the lamina.Compared with the traditional lamina hook system,the improved lamina hook system can effectively reduce the displacement in all directions and range of motion of lumbar spondylolysis,therefor can significantly reduce the stress of internal fixation and vertebral body and has better biomechanical performance.