BACKGROUND:Transpedicular transdiscal lumbar screw is a new type of spinal minimally invasive internal fixation technology.Compared with traditional bilateral pedicle screws,only one screw is needed to fix one segment on one side.It has the characteristics of being more economical,less trauma and easy to operate.However,studies on the application of transpedicular transdiscal lumbar screws combined with transforaminal lumbar interbody fusion(TLIF)and fixation are still rare. OBJECTIVE:To evaluate the effect of TLIF combined with various surgery methods on stress distribution of cage,fixation,disc lower and endplate and range of motion of lumbar vertebrae by constructing three kinds of finite element models including modified TLIF(cage alone)model,modified TLIF combined with bilateral pedicle screw(cage+BPS)model and modified TLIF combined with bilateral transpedicular transdiscal lumbar screw(cage+BTPTDS)model. METHODS:The CT images of the adult lumbar spine were used to establish the three kinds of TLIF finite element models:cage alone,cage+BPS and cage+BTPTDS using software Mimics,Geomagic and SolidWorks.ANSYS Workbench was used to simulate the application of six different motion loads of human body flexion and extension,left and right bending,and left and right rotation to calculate stress distribution and the changes in the range of motion of the lumbar spine of the cage,fixation,endplate and disc of the three lumbar spine surgery models and to compare the effects of three surgical options on the biomechanical effects of the lumbar spine. RESULTS AND CONCLUSION:(1)The cage alone model,cage+BPS model and cage+BTPTDS model were constructed successfully.(2)In flexion and lateral bending conditions,the maximum stress of the cage of cage+BTPTDS model was smaller than that of the cage alone model and a little greater than that of the cage+BPS model.In the extension condition,the maximum stress of the cage of the cage+BPS model was obviously smaller than that of the other two models.When it came to rotating condition,the maximum stress of the cage in the cage+BPS model and the cage+BTPTDS model presented no obvious difference,which was both smaller than the cage alone model.(3)The maximum stress of fixation of the cage+BTPTDS model was obviously bigger than the cage+BPS model in flexion and extension conditions,close to the cage+BPS model in lateral bending conditions,and smaller than the cage+BPS model in rotation conditions.(4)The maximum stress of the lower endplate of the fusion segment of the cage+BPS model was between the two other models.(5)In terms of the range of motion,the cage+BTPTDS model presented no obvious difference with that of the cage+BPS model at flexion and extension,left and right bending,and left and right rotation.(6)It is concluded that modified TLIF combined with transpedicular transdiscal lumbar screw provides stable support for the vertebral body of the fusion segment,ensures the motion range of the lumbar spine and has a good biomechanical effect.