Biomechanical comparison of oblique lateral interbody fusion with interspinous versus other fixation techniques: A finite element study

BACKGROUND: Oblique lateral interbody fusion (OLIF) is a minimally invasive technique for treating degenerative lumbar diseases, yet the optimal supplemental fixation strategy remains debated. Interspinous fixation systems (ISFS) offer a less invasive alternative to conventional pedicle screw-based constructs, but their biomechanical performance when combined with OLIF is not well characterized. METHODS: A validated finite element model of the L3-S1 lumbar spine was used to simulate OLIF at L4-L5 with 5 fixation configurations: stand-alone, unilateral pedicle screw fixation, bilateral pedicle screws fixation (BPSF), ISFS, and ISFS combined with lateral screw fixation (ISFS + lateral screws fixation [LSF]). Range of motion (ROM) at the fused and adjacent segments, along with von Mises stress distributions on the endplates, interbody cage, and instrumentation, were evaluated under a 500 N compressive preload and 10 N·m pure moments in flexion, extension, lateral bending, and axial rotation. RESULTS: All fixation constructs reduced ROM at the fused-segment compared to the intact model. BPSF and ISFS + LSF provided the greatest stability across all loading directions, with ROM reductions exceeding 80% in most postures. ISFS alone effectively stabilized the segment during flexion-extension, but was less effective under rotational and lateral bending loads. Stand-alone OLIF exhibited the highest cage stresses and the largest residual ROM, indicating increased risk of instability and subsidence. ISFS + LSF distributed stress more evenly across the cage and endplates, comparable to BPSF, while reducing stress concentration on the spinous process base during lateral bending. Adjacent segment ROM and endplate stress remained similar across all models and the intact condition. CONCLUSION: OLIF combined with interspinous fixation, particularly ISFS + LSF, provides a favorable biomechanical profile by enhancing segmental stability and reducing implant-related stress concentrations, while preserving adjacent segment kinematics. ISFS + LSF may serve as a less invasive alternative to BPSF, offering balanced stability and load sharing. ISFS alone is suitable for flexion-dominant loading environments, whereas BPSF remains the most robust option for multiplanar stability at the cost of increased surgical trauma. These findings support the selective use of interspinous fixation in OLIF based on patient-specific biomechanical demands.