Risk Factors for Subsidence Following Anterior Lumbar Interbody Fusion

Study Design: Retrospective cohort Objective: Anterior lumbar interbody fusion (ALIF) may be complicated by subsidence, which can lead to significant morbidity including pain, disc space collapse, neural compression, segmental kyphosis, instability, and vertebral body fracture. This study sought to identify patient and procedural risk factors for subsidence in patients undergoing ALIF. Methods: This study analyzed consecutive patients who underwent ALIF at a single institution with a minimum of 2 years follow-up. Patients were grouped as either Non-Subsidence (NS-ALIF) or Cage Subsidence (CS-ALIF) based on the final postoperative radiograph. Demographic variables, operative characteristics, and radiographic outcomes were evaluated to identify significant predictors on univariate and multivariate statistics. Results: 144 patients (170 levels) were included with an average follow-up of 50.70 +/- 28.44 months (4.23 years). The incidence of subsidence was 22.94% (39/170 levels). On univariate statistics, the CS-ALIF group was significantly older (P=.020), had higher BMI (P=.048), worse ASA (P=.001), higher prevalence of comorbid osteoporosis (P<.001), and a more anteriorly placed interbody device (P=.005). On multivariate analysis, anterior cage placement remained the only significant predictor (OR: 1.08, 95% CI: 1.03-1.14; P=.003). There was a significantly higher rate of subsequent adjacent segment surgery among the CS-ALIF group (P=.035). Conclusion: Factors contributing to subsidence in ALIF included older age, higher BMI, severe ASA, and osteoporosis, while anterior cage placement remained the only independent predictor on multivariate analysis. Subsidence was associated with a higher rate of subsequent adjacent segment surgery. Surgical technique should optimize placement of the interbody cage and avoid overstuffing the disc space.