Impact of cage position in posterior lumbar interbody fusion on cage subsidence in patients with asymmetric Modic changes and analysis of related risk factors

OBJECTIVE: To assess the influence of interbody cage position in PLIF on subsidence risk among asymmetric Modic changes (AMC) patients and identify associated risk factors. METHODS: This retrospective analysis included 69 AMC patients undergoing single-level PLIF (January 2022-December 2023, single-surgeon cohort). Postoperative X-ray categorized patients into Modic Same Side (MSS) and Modic Opposite Side (MOS) groups based on cage position. Collected data encompassed demographics, surgical parameters, imaging metrics, and clinical outcomes. Pearson correlation, multiple regression, and ROC curve analysis (predicting subsidence ≥ 25%) were performed using SPSS (significance: P < 0.05). RESULTS: Cage subsidence rates did not differ significantly between MOS and MSS groups at any follow-up (P > 0.05). Both groups exhibited significant VAS/ODI improvement (P < 0.001), with no intergroup differences. Pearson analysis revealed significant correlations between 1 year subsidence and Modic grade, BMI, blood loss, and 3 month subsidence. Multiple regression confirmed Modic grade and 3 month subsidence as independent predictors of 1 year subsidence (P < 0.05). ROC analysis determined a 3 month subsidence cutoff of 12.5% optimally predicted 1 year subsidence ≥ 25% (AUC = 0.786, P < 0.001). CONCLUSION: Cage position does not significantly affect subsidence in PLIF for AMC patients, with PLIF effectively alleviating symptoms. Higher Modic grades correlated with reduced subsidence. BMI and blood loss are independent predictors. Early subsidence > 12.5% at 3 months predicts significant risk (≥ 25%) at 1 year, underscoring the necessity of early radiographic surveillance for timely intervention.