Risk of subsidence following ACDF with the coalition™ (Globus Medical) cage: a multivariable analysis identifying preoperative radiculopathy as the primary risk factor

BACKGROUND: The Coalition (Globus Medical) hybrid PEEK-titanium cage has been widely utilized in our practice for Anterior Cervical Discectomy and Fusion (ACDF) over a 5-year period. A preliminary review of all the cases that we performed in these five years show to us an unexpectedly high rate of postoperative cage subsidence with the Coalition (Globus Medical) stand-alone cage. This prompted a formal investigation, the purpose of this study was, therefore, to systematically determine the true rate of subsidence for the Coalition cage in our cohort and to identify the independent risk factors that could explain this finding. METHODS: We conducted a retrospective analysis of 70 consecutive patients who underwent ACDF with the Coalition cage between 2018 and 2023. Data on demographic, clinical, and surgical variables were collected. The primary outcome was cage subsidence (≥ 3 mm) assessed on lateral radiographs at a mean follow-up of 28.8 months (range 12-48). Independent predictors were identified through a multivariable logistic regression model constructed using the purposeful selection of covariates strategy, a multi-step iterative process that accounts for both statistical significance and confounding effects. RESULTS: The overall patient-based subsidence rate was 38.6% (27 of 70 patients) at a mean radiographic follow-up of 28.8 months. Interrater reliability for subsidence assessment was substantial (Kappa = 0.759). In the multivariable analysis, preoperative diagnosis of radiculopathy was identified as the only independent predictor of subsidence, with an Adjusted Odds Ratio of 3.51 (95% CI: 1.13-10.91, p = 0.029). Contrary to initial assumptions, multi-level surgery (p = 0.441), smoking status (p = 0.615), and implant dimensions were not significant predictors in this cohort. CONCLUSION: The Coalition cage demonstrated a high rate of subsidence in this series. A preoperative diagnosis of radiculopathy was the primary independent risk factor for this outcome, rather than multi-level fusion or specific implant characteristics. These findings suggest that the biomechanical requirements of disc height restoration in patients with radiculopathy may predispose them to higher subsidence rates when utilizing this specific standalone integrated fixation device.