Biomechanical advantage of anterior over central cage placement in XLIF with bilateral pedicle screw fixation: a finite element analysis

OBJECTIVE: This finite element study aimed to compare the biomechanical differences between anterior and central cage placement in L3-L4 XLIF supplemented with bilateral pedicle screw fixation, to evaluate the biomechanical impact of cage positioning on minimizing cage subsidence risk. METHODS: Three L1-L5 finite element models were developed from healthy volunteer CT data: intact (Group A), L3-L4 XLIF with anterior cage placement (Group B), and central cage placement (Group C). Loads simulating flexion, extension, lateral bending, and rotation were applied. Segmental stability and cage stress distribution were analyzed. RESULTS: Both surgical groups markedly decreased range of motion (ROM) at L3-L4 compared to Group A. The peak stress on the cage was consistently lower in Group B than in Group C across all motions. The screw-rod system stress in Group B was higher than in Group C in all motions except flexion. Facet joint stress in adjacent segments was higher in Group C than in Groups A and B. CONCLUSION: In this finite element model, anterior cage placement was associated with lower cage stress and higher posterior instrumentation stress than central placement, while segmental stability remained similar. These results indicate a different load-sharing pattern and suggest potential biomechanical differences in adjacent segment loading. Further research is needed to clarify the clinical implications.