Higher screw-to-cage length ratios in standalone lateral interbody fusion using integrated, expandable implants provide more predictable outcomes with less variability: A 2-year follow-up study.

Background Context: Lateral Lumbar Interbody Fusion (LLIF) is widely used for degenerative spinal disorders. Standalone LLIF with expandable cages integrating plate-screw fixation (eLLIFp) has emerged to address disc degeneration and adjacent segment disease while reducing the need for posterior fixation. Biomechanical data suggest greater stability with longer screws, but the clinical impact of screw-to-cage length ratios remains unclear. This study evaluates outcomes following eLLIFp and investigates whether screw-to-cage ratios influence results. Methods: Eighty-one patients (87 levels) underwent eLLIFp, mean age 63.8±10.8 years (49.4% female), BMI 27.7±4.9 kg/m². Common levels treated were L2/3 (35%) and L3/4 (29%). Mean retractor time was 30.2±5.5 min. Retrospective analysis of prospectively collected data examined integrated screw length (30-60 mm) and cage length (50-65 mm). Screw-to-cage ratios were grouped into tertiles: Low (0.46-0.75, n=36), Medium (0.76-0.82, n=18), and High (0.83-1.0, n=27). Outcomes included pain (VAS), disability (ODI), quality of life (SF-12), and fusion status on 12-month CT. Minimum follow-up was 2 years. Results: At 12 months, all patients showed significant improvement (p<0.0001) [VAS back: 7.6→0.9; VAS leg: 6.3→0.7; ODI: 25.7→5.1; SF-12 PCS: 29.9→49.2; MCS: 37.3→55.6]. Improvements were comparable across tertiles, though the high-ratio group exhibited less variability in leg pain outcomes. Fusion was achieved in 79/81 (97.5%) patients. Complications occurred in 5 (6.2%): 3 neurological (motor radiculopathy, radicular pain, transient thigh numbness) and 2 symptomatic nonunions requiring posterior fixation, both with lower screw-to-cage ratios (0.7). Conclusions: Higher screw-to-cage ratios (0.83-1.0) in standalone eLLIFp constructs may enhance consistency in leg pain relief without increasing complications. Maximizing screw length relative to cage dimensions may optimize outcomes and reduce variability in standalone LLIF.