Biomechanical investigation of the hybrid lumbar fixation technique with traditional and cortical bone trajectories in transforaminal lumbar interbody fusion: finite element analysis

OBJECTIVE: To compare the biomechanical performance of the hybrid lumbar fixation technique with the traditional and cortical bone trajectory techniques using the finite element method. METHODS: Four adult wet lumbar spine specimens were provided by the Department of Anatomy and Research of Xinjiang Medical University, and four L1–S1 lumbar spine with transforaminal lumbar interbody fusion (TLIF) models at L4–L5 segment and four different fixation techniques were established: bilateral traditional trajectory screw fixation (TT–TT), bilateral cortical bone trajectory screw fixation (CBT–CBT), hybrid CBT–TT (CBT screws at L4 and TT screws at L5) and TT–CBT (TT screws at L4 and CBT screws at L5). The range of motion (ROM) of the L4–L5 segment, von Mises stress of cage, internal fixation, and rod were compared in flexion, extension, left and right bending, and left and right rotation. RESULTS: Compared with the TT–TT group, the TT–CBT group exhibited lower ROM of L4–L5 segment, especially in left-sided bending; the CBT–TT group had the lowest ROM of L4–L5 segment in flexion and extension among the four fixation methods. Compared with the CBT–CBT group, the peak cage stress in the TT–CBT group was reduced by 9.9%, 18.1%, 21.5%, 23.3%, and 26.1% in flexion, left bending, right bending, left rotation, and right rotation conditions, respectively, but not statistically significant (P > 0.05). The peak stress of the internal fixation system in the TT–CBT group was significantly lower than the other three fixation methods in all five conditions except for extension, with a statistically significant difference between the CBT–TT and TT–CBT groups in the left rotation condition (P = 0.017). In addition, compared with the CBT–CBT group, the peak stress of the rod in the CBT–TT group decreased by 34.8%, 32.1%, 28.2%, 29.3%, and 43.0% under the six working conditions of flexion, extension, left bending, left rotation, and right rotation, respectively, but not statistically significant (P > 0.05). CONCLUSIONS: Compared with the TT–TT and CBT–CBT fixation methods in TLIF, the hybrid lumbar fixation CBT–TT and TT–CBT techniques increase the biomechanical stability of the internal fixation structure of the lumbar fusion segment to a certain extent and provide a corresponding theoretical basis for further development in the clinic.