The Three-dimensional Finite Element Analysis Of Minimal Invasive Transforaminal Lumbar Interbody Fusion Using Different Internal Fixations

Objective (1)To establish the nonlinear finite element model(FEM)of L3-L5using the normal human spinal CT data;(2) To establish the nonlinear finiteelement model(FEM) of transforaminal lumbar interbody fusion using three differentinternal fixations in lumbar and compare the difference of biomechanical propertyamong these fixations using the finite element method.Methods In this study, a detailed L3-L5three-dimensional nonlinear FEM of anormal adult man was established with the aid of MIMICS and ANSYS from thinsection CT images(1mm)．The model was validated in contrast to the biomechanicalbehaviors of previous cadaver spine, meanwhile the stress distribution of the intactfinite element model was recorded. Based on the normal finite element model，the threeoperative models including BPS,UPS and UPS+TLFS were built up．After loadings wasemployed on all models，we recorded range of motions of two segments and stressdiagrams and the Von Mises stress of annulus fibrosus,interbody fusion cage andscrews．Results (1)The range of motion of L3-4segment was7.3°in flexion,3.1°inextension,2.3°in left rotation,2.2°in right rotation,4.3°in left bending and4.6°in right bending respectively; the range of motion of L4-5segment was8.1°inflexion,3.8°in extension,2.2°in left rotation,2.0°in right rotation,5.5°in leftbending and5.8°in right bending respectively. The range of motion values of thisresearch was among the95%confidence interval of Panjabi’s values and slightly lessthan Yamamoto’s,by which the model validation was confirmed;(2)Compared with theintact model, all the operative models including BPS,UPS and UPS+TLFS increased thestiffness of fixation segment in all direction of motion, the most stiff model is BPS,andthe lowest is UPS model.(3)In UPSF model,the maximum stress of screws andinterbody fusion cage were highest in extension, bending and rotation,especially therewere stress concentration in right rotation and right bending.(4)In all direction of motion,the stress of UPS+TLFS model was slightly lower than BPS model but slightly higher than BPSF model.(5)The ROM and stress of annulus fibrosus didn’t increase obviouslyin adjacent segment.Conclusion (1) The nonlinear finite element model of normal human in L3-5wasestablished and whose validation was confirmed.(2) Unilateral pedicle screwssupplemented with contralateral TLFS fxation was considered appropriate fixation forminimal invasive transforaminal lumbar interbody fusion for the reasons that it mayminimize the biomechanical drawbacks of UPS and likely achieved the biomechanicalproperty of UPS.(3)Compared with BPS model, UPS+TLFS model reduced the stressshielding, and promoted the interbody fuion.