Radiological Alignment Trajectories and Late Functional Outcomes After Three-Level ACDF: A Single-Center Cohort Study

Background: Three-level anterior cervical discectomy and fusion (ACDF) is widely used for multilevel cervical degenerative disc disease; however, the relationship between postoperative alignment trajectories, adjacent segment degeneration (ASD), and late patient-reported outcomes remains incompletely defined. This study evaluated plane-specific radiological alignment changes, MRI-based ASD, and late functional outcomes in a homogeneous three-level ACDF cohort. Methods: This single-center observational cohort included 29 patients who underwent three-level ACDF between January 2018 and December 2023 and had complete radiographic follow-up. Radiological data were collected retrospectively from institutional records and imaging archives. Cervical sagittal and coronal alignment were assessed using Cobb angles on radiographs obtained preoperatively and at 6 months, 1 year, and 2 years postoperatively. ASD was evaluated at the superior adjacent segment on 2-year MRI. Late patient-reported clinical outcomes were assessed at a mean follow-up of 42.6 ± 6.8 months using the Visual Analog Scale (VAS), Neck Disability Index (NDI), and Nottingham Health Profile (NHP). Results: Sagittal Cobb angle changed significantly over time (χ²(3) = 12.60, p = 0.006; Kendall's W = 0.145), whereas coronal Cobb angle showed a statistically significant reduction over time, although the absolute magnitude of change was small (χ²(3) = 28.74, p < 0.001; Kendall's W = 0.330). Lower sagittal Cobb angle correlated with worse NDI (r = -0.46, p = 0.004), and greater coronal Cobb angle correlated with worse physical activity scores (r = 0.52, p = 0.006). Higher Pfirrmann grade correlated with worse NDI (r = 0.49, p = 0.004) and pain scores (r = 0.44, p = 0.021). In exploratory regression analysis, sagittal Cobb angle and Pfirrmann grade were retained in the model for NDI, but these findings should be interpreted as hypothesis-generating. Conclusions: After three-level ACDF, sagittal and coronal alignment followed different postoperative trajectories. Lower sagittal alignment and greater adjacent disc degeneration were associated with worse late neck-related disability. However, given the modest sample size and exploratory nature of the regression analysis, these findings should be interpreted as hypothesis-generating. Larger prospective studies are needed to confirm whether sagittal alignment and MRI-based adjacent segment degeneration independently contribute to late functional outcomes.