Digital Simulation And Biomechanical Study Of Double Pedicle Screw Technique For Unstable Thoracolumbar Burst Fractures

Objective: To introduce the specific implementation of the Double Pedicle Screw(DPS)technique for treating unstable thoracolumbar burst fractures(UTBF),and explore its anatomical feasibility and biomechanical characteristics in UTBF treatment through digital simulated screw placement and finite element simulation analysis.Methods: Before conducting finite element analysis,100 healthy adult T10-L3 segment CT data were collected from the radiology department database.The width(PW)and height(PH)of each pedicle were measured and MIMICS software was used to simulate the placement of DPS in each pedicle one by one.The accuracy of the DPS screw position was classified into four categories,A,B,C,and D,according to the accuracy classification method of thoracolumbar-sacral pedicle screws,with categories A and B considered as accurate positions.Finally,the success rate of screw placement was calculated,and the relationship between PW,PH,and the success rate of screw placement was analyzed.Subsequently,ideal CT data was selected to establish a T10-L2 finite element model.A wedge osteotomy was performed on the T12 vertebral body,and the posterior ligament complex of the same segment was removed to simulate the UTBF.Five different fixation models were established for analysis,including short-segment fixation(SSF),long-segment fixation(LSF),short-segment satellite rod fixation(SRF),long-segment satellite rod fixation(LRF),and short-segment double pedicle screw fixation(DPS).The analysis of each model was conducted in Ansys Workbench 2021 R2 software,and the range of motion(ROM)of T11-L1 and the maximum von Mises stress on the internal fixation system(IFS)were recorded.Finally,the biomechanical performance of the DPS structure was analyzed and discussed.Results: Among the 1200 pedicle screws simulated,46.2% were graded as a,36.2% as B,15.1% as C,and 2.5% as D,resulting in an overall success rate of 82.4%.The success rates for double pedicle screw insertion in the T10-L3 vertebrae were 77.5%,83.0%,84.0%,80.0%,80.5%,and 89.5%,respectively.When the PW was above 6mm,the success rate of double screw insertion was over 98%,and when the PH was above 12 mm,the success rate of double screw insertion was over 91%.In finite element analysis,the DPS structure performed the best in reducing the range of motion(ROM),with a maximum improvement of 45.9% over other structures.Followed by the LRF,SRF,LSF,and SSF.The DPS structure also had a significant advantage over other structures in terms of maximum stress in the internal fixation system(IFS),with a maximum improvement of 61.5% over other structures.Both types of satellite rod structures performed well in reducing ROM.Among them,the LSR model exhibits stronger rigidity than the DPS model under lateral bending conditions.However,neither of the two satellite rod structures can reduce the maximum stress of the IFS like the DPS structure.Conclusion: The feasibility of implementing DPS technology in the thoracolumbar spine segment depends on the height and width of the pedicle.The higher and wider the pedicle is,the higher the success rate of the implementation.The biomechanical performance of DPS technology in treating UTBF is superior to traditional internal fixation,which helps to increase the stability of the internal fixation and reduce stress concentration in the internal fixation system,thereby reducing the risk of screw loosening and internal fixation failure.The use of DPS technology can reduce the number of fixed segments in the vertebral body,effectively retaining more mobile segments in the spine,and better ensuring the efficacy of UTBF cases.