Influence Of PLIF And TLIF On The Stabilization Of Lumbar Spine By Finite Element Analysis

Background With the rapid growth of computer technology, finite element analysis method has been applied to the research in every field of clinical medicine at an alarming rate. For the first time finite element analysis was applied in orthopaedic biomechanics research to estimate the stress of the complex shape, load and substantial properties in the 1970 s. It is the basic trend of orthopaedic biomechanics development that applying finite element analysis to orthopaedic biomechanics and it also promotes the further development of finite element. The 21 st Century is the era of rapid development of minimally invasive spinal surgery technology, but the basic research is relatively lack, the use of finite element analysis to study a variety of new technology is very necessary. Objective To establish a finite element model of lumbar spine and to analyze the effect of PLIF and TLIF at the L3-4 segment on the stability of lumbar spine by using finite element method. Methods Complete thin scan CT images of a 30 years old healthy man from lumbar 1 to the sacrum vertebral body were chosen from China-Japan United hospital of Jilin university, and imported the original image data which was DICOM format into MIMICS16.0 software, preliminary lumbar spine three-dimensional model was established. We reprocessed and assemblied it in Geomagic Studio12.0, Pro/E, 5.0, then we simulated the operations of PLIF and TLIF and placed the pedicle screws and cage, three intact three-dimensional model were initially established. We imported data into ANSYS software for further processing, 3D finite element model was finally established. Under the specific boundary conditions and loads applied the three models, we got the ROM of 6 kinds of motions and the maximum stress changes of the upper and lower end plate and screws. At last we analyzed and compared the stabilization of L3-4 PLIF model, TLIF model and intact lumbar spine model. Results 1 We compared the results of range-of-motion of finite element intact lumbar model with those from the cadaveric study in all six loading cases. We found a good agreement between our results and the reported results, which verified the rationality of the finite element models. 2 The range of motions at the L3-4 segment of the PLIF and TLIF models decrease in all six loading cases compared with the intact model. Range of motion of the PLIF model was larger than that of the TLIF model under the extension condition. However, the range of motions at the L3-4 of the PLIF and TLIF had no significant differences under the six loading conditions. 3 In the TLIF and PLIF models, almost all of the motion conditions were the maximum stress of the upper end plate of the L4, which was greater than the maximum stress of the lower end plate of L3. In general, the maximum stress of the TLIF model was smaller than that of the PLIF model in both the lower end plate of L3 and the upper end plate of the L4. 4 The lower screw in the PLIF model bore greater stress and more of the risk of breaking off. The maximum screw stress of the PLIF model under each motion state was greater than that of the corresponding TLIF model. In TLIF model, the maximum stress of left screw in any state of motion was greater than the corresponding right-hand screw no matter on the upper or lower nail. Conclusions 1 The results of this study showed that the ROM of six kinds of movement conditions made no differences and could achieve the similar stability between the TLIF model and the PLIF model. 2 Either in the TLIF or in the PLIF models, almost each of the motion condition was the maximum stress of the upper end plate of the L4, which was greater than the maximum stress of the lower end plate of L3, it could be concluded that the fusion was more easy to subside on the upper end plate instead of the lower end plate. 3 In general, the TLIF surgery with resection one side of the articular process had reduced the stress on the end plate with respect to the PLIF surgery with resection of the posterior structure, and the probability of the occurrence of the PLIF fusion subsidence was less than that of the TLIF. 4 In TLIF model the maximum stress of left screw in any state of motion was greater than the corresponding right-hand screw no matter on the upper or lower nail. The maximum screw stress of the PLIF model under each motion state was greater than that of the corresponding TLIF model. 5 Posterior structures such as vertebral lamina, spinous process and posterior ligament complex played a more important role in the stabilization of the lumbar spine than unilateral articular processes.