Design And Finite Element Biomechanical Study Of Z-type Cross Link.

Objective:The purpose was to design a new Z-type cross link for spinal internal fixation system.And to compare the stability and stress distribution of three different cross-link configurations with a 3D finite element model of L3 burst fracture.Method:A 3D finite element model of L1-L5(a hypothetical L3 vertebra burst fracture.)was used to investigate the biomechanical behavior of 2 level segmental spine pedicle screw fixation with three different kinds of cross-links: horizonal double cross link(HBC),X-type cross link(XC)and Z-type cross link(ZC).An axial pressure of 200 N and moment force of 10Nm)were applied after the connection of different cross links,the motion range of the fixed segment vertebral body in flexion,extension,lateral bending and axial rotation of the range of motion(ROM),and the peak value of Von Mises stress in vertebral body,internal fixation system and cross links was measuredResult:The range of motion(ROM)in flexion was 3.7025°,3.6155°,3.397°;in lateral bending was 0.8965 °,0.8965 °,0.8306 °;and in axial rotation was 1.921°,1.8859°,1.7032°in the HBC,XC and ZC model respectively.The stability of ZC was better than that of the HBC and XC.Especially for the most significant anti axial rotation ability,the stability of ZC is 28.1% higher when compared with HBC,and 16.3% higher than XC.The Von Mises stress distribution results show that the Z-type cross link can reduce the stress peak of vertebral fracture and its adjacent vertebral bodies in various conditions: in flexion condition,ZC can make the L2 vertebral stress decreased by 64.9% and 27.8% when compared with HDC and XC respectively;in axial rotation condition which the cross link even played a major role,ZC can make the L2 vertebral stress peak decreased by 48.6% compared to HDC,and decreased by 32.6% compared to XC.Conclusion:Z-type cross link can increase the stability of the spinal internal fixation system,especially in the aspect of axial rotation,which can provide stronger stiffness.Z type cross link can also reduce the stress peak of vertebral body to some extent,which is more obvious when in the flexion and axial rotation,which may reduce the possibility of bone injury.