Objective:

The finite element method was used to investigate the biomechanical adjustments of adjacent and fixed segments after lumbar fusion and fixation with traditional trajectory (TT) and cortical bone trajectory (CBT) screws.

Methods:

The model used was a validated nonlinearly L3-S1 finite element model. Interbody fusion cages and two types of screws were used to work on the L4-5. To simulate flexion, extension, lateral bending, and axial rotation, all models were loaded in three planes with a compressive pre-load of 400 N and a bending moment of 7.5 N/m. Under various loading conditions, the range of motion (ROM), peak Von Mises stress of the vertebral body, stress of the intervertebral disc, stress of the facet joints, stress of the endplate, and stress of internal fixation were compared.

Results:

In all instrumentation models, the ROM at fixed segments decreased. At adjacent segments, the ROM of the CBT model was higher than that of the TT model. The CBT model had a higher peak Von Mises stress of the L4 and L5 vertebral bodies, as well as higher stress of internal fixation, than the TT model. Furthermore, as compared to the TT model, the CBT model’s facet joint and endplate stress were lower at fixed segments but higher at adjacent segments. The stress on the L3-L4 and L5-S1 intervertebral discs in the CBT and TT models, on the other hand, was nearly equivalent.

Conclusion:

At the fixed section, CBT may provide slightly better stability, endplate tension, and facet joint stress than TT. The higher ROM, endplate stress, and facet joint stress of CBT in adjacent segments, on the other hand, should be taken into account in the future.