Visceral Adiposity Index Outperforms Body Mass Index in Predicting Early Cage Subsidence Following Lumbar Interbody Fusion: A Retrospective Cohort Study

Abstract Background Conventional anthropometric indices like Body Mass Index (BMI) often fail to accurately capture the metabolic risks affecting bone quality in spinal surgery. This study aimed to investigate the predictive value of the Visceral Adiposity Index (VAI) for early cage subsidence following lumbar interbody fusion (LIF) and to compare its diagnostic accuracy with traditional obesity metrics. Methods A retrospective cohort study was conducted on 347 patients who underwent 1- or 2-level LIF. Early cage subsidence was defined as ≥ 2 mm sinking into the adjacent vertebral endplate. VAI was calculated based on baseline anthropometric and lipid parameters. Multivariate logistic regression models were employed to identify independent risk factors. A restricted cubic spline (RCS) model and receiver operating characteristic (ROC) curves were utilized to evaluate the dose-response relationship and predictive performance. Results Early cage subsidence occurred in 83 patients (23.9%). In the fully adjusted multivariate model, elevated VAI (aOR = 1.58, 95% CI: 1.25–2.01, P < 0.001), older age, and lower BMD T-score remained independent predictors, whereas BMI and diabetes lost their statistical significance. RCS analysis revealed a significant non-linear threshold effect (P for non-linearity = 0.012), showing a sharp increase in subsidence risk once VAI exceeded 2.40. ROC analysis demonstrated that VAI (AUC = 0.785, optimal cut-off > 2.85) possessed significantly superior predictive accuracy compared to BMI (AUC = 0.642, P = 0.002) and waist circumference (AUC = 0.685, P = 0.015). Subgroup analyses confirmed the robust predictive value of high VAI across various clinical demographics. Conclusions Elevated preoperative VAI is a novel and powerful independent predictor of early cage subsidence after LIF, significantly outperforming BMI. These findings suggest that the deleterious metabolic microenvironment of visceral adiposity, rather than pure mechanical loading, primarily compromises endplate integrity. VAI can serve as an invaluable, cost-effective tool for preoperative risk stratification.