Finite Element Analysis Of Lumbar Vertebra Biomechanics After Transforminal Lumbar Interbody Fusion Combined With Bilateral Transpedicular Transdiscal Lumbar Screw Fixation

Objective: To evaluate the effect of TLIF(Transforaminal Lumbar Interbody Fusion)combined with various fixations on stress distribution of cage,internal fixations,intervertebral disc,lower endplate and range of motion of lumbar by constructing three kinds of L3-5 interbody fusion finite element models including TLIF without fixation(cage alone)model,TLIF combined with Bilateral Pedicle Screw(cage+BPS)model and TLIF combined with Bilateral Transpedicular Transdiscal lumbar Screw(cage+BTPTDS)model after constructing the L3-5 finite element model.Methods: The CT images of lumbar spine of a normal adult male were used to establish the L3-5 finite element model by three programs: Mimics 21.0,Geomagic 17.0 and Solid Works 2017.Then the constraints and loads were set by ANSYS Workbench 17.0 to verify the validity of the model.The software Solid Works 2017 was then used to construct three kinds of L3-5 interbody fusion finite element models: cage alone model,cage+BPS model and cage+BTPTDS model after the validation of validity.Six different loads of lumbar in flexion and extension,lateral bending and rotation were applicated on the models by ANSYS Workbench 17.0 to calculate the stress of cage,internal fixations,intervertebral disc and lower endplate and the difference of lumbar range of motion.Then compare the differences of the effects of three surgical options on the biomechanical effects of lumbar spine.Results: 1.L3-5 finite element model was constructed successfully and verified the validity of the model.2.Three kinds of L3-5 interbody fusion finite element models: cage-alone model,cage+BPS model,cage+BTPTDS model were constructed successfully.3.In flexion and lateral bending conditions,the maximum stress of cage of cage+BTPTDS model was smaller than that of cage alone model and a little more greater than that of cage+BPS model.In extension condition,the maximum stress of cage of cage+BPS model was obvious smaller than that of two other models.When it came to rotating condition,the maximum stress of cage in cage+BPS model and cage+BTPTDS model presented no obvious difference,which were both smaller than cage alone model.4.The maximum stress of fixation of cage+BTPTDS model was close to cage+BPS model in lateral bending conditions,obviously bigger than cage+BPS model in flexion and extension conditions and smaller than cage+BPS model in rotation conditions.5.The maximum stress of lower endplate of fusion segment of cage+BPS was between the two other models.6.Cage alone model and cage+BPS model had similar maximum stress of intervertebral disc and lower endplate in non-fusion segment,slightly greater than cage+BPS model.7.In terms of range of motion,cage+BTPTDS model presented no obvious difference with that of cage alone model and was greater than cage+BPS model at various conditions.Conclusion: 1.The validity of the L3-5 finite element model that constructed in this study was well verified and the results were reliable for lumbar spine biomechanical experiments.2.Cage+BPS model and cage+BTPTDS model had similar biomechanical effects of lumbar spine and both were superior to cage alone model.3.Compared with BPS,BTPTDS is less invasive,economical and easy to perform.It also provides good stability of the fusion segment and ensures overall lumbar range of motion which has a good biomechanical effect.