Heterogeneity in radiographic fusion criteria for ACDF in FDA IDE trials: A systematic review

Objectives: Radiographic fusion is a determinant of surgical success following anterior cervical discectomy and fusion (ACDF). However, reported fusion rates in the literature vary widely. We hypothesize this is due to heterogeneity in how fusion is assessed. To investigate this, we conducted a systematic review of FDA Investigational Device Exemption (IDE) clinical trials to evaluate variation in fusion assessment methods. Materials/Methods: A systematic review was conducted in accordance with the Preferred Reporting Items and Meta-analyses guidelines and protocol to identify FDA IDE clinical trials involving patients undergoing one- or two-level ACDF. The primary variable of interest was radiographic fusion criteria. The secondary variable of interest was the reported fusion rate. Patient demographics, surgical details, and outcomes at follow-up intervals were extracted. Statistical analysis was performed using unpaired t tests, with significance set at P ≤0.05. Results: Eleven FDA IDE clinical trials with 1926 patients (84.8% undergoing one-level ACDF and 15.2% undergoing two-level ACDF) were identified, with a mean age of 45 years for one-level ACDF patients and 47 years for two-level patients. Significant variation was observed in the fusion assessment criteria among the FDA trials. The criteria included the presence of bridging bone on radiographs, radiolucency in <%50 of the graft-vertebra, and variable motion criteria (angular and translational) on radiographs. None of the studies routinely used CT scans or strict interspinous motion criteria (<1 mm) on flexion/extension radiographs. Using the reported criteria within the study, at 24 months, the weighted mean fusion rate for one-level ACDF was 91%, increasing to 97% at 84 months. For two-level ACDF, fusion rates increased from 81% at 24 months to 92% at 84 months. Conclusions: FDA IDE trials exhibited significant variability in fusion assessment criteria and relied on unreliable indicators, like high angular and translational motion, suggesting overestimation of fusion rates. The lack of consistency hampers comparison of rates and suggests that evidence-based consensus criteria be adopted.