Global, Regional, and Local Radiological Changes after Single-Level Anterior Cervical Discectomy and Fusion: A Quantitative Magnetic Resonance Imaging Study of Index and Adjacent-Level Canal Morphology

Objective: To characterize global, regional, and local radiological changes after single-level anterior cervical discectomy and fusion (ACDF), focusing particularly on changes in spinal canal anteroposterior (AP) diameter and ligamentum flavum (LF) thickness quantified by magnetic resonance imaging (MRI) at the index and adjacent levels.Methods: We retrospectively analyzed 26 patients who underwent single-level ACDF and had paired preoperative and postoperative measurements obtained from radiographs and MRI.The median interval from surgery to postoperative MRI was 4 months (range, 1-33 months).We assessed the C2-7 Cobb angle, C2 angle, and T1 slope as global parameters and the index segmental angle as the regional parameter.Local MRI measurements comprised canal AP diameter and LF thickness at the index, upper adjacent, and lower adjacent levels, as well as adjacent disc height.Paired t-tests with Holm adjustment were used to compare preoperative and postoperative measurements, and exploratory associations among changes were assessed using Spearman's rank correlation analysis with Benjamini-Hochberg false discovery rate (FDR) correction.Results: The patients had a mean age of 61.7 ± 12.8 years and a mean body mass index of 25.5 ± 3.3 kg/m 2 .At the index level, canal AP diameter increased from 6.13 ± 1.83 to 8.66 ± 1.80 mm (mean change, +2.53 ± 1.32 mm; p < 0.001), whereas LF thickness decreased from 3.43 ± 0.86 to 3.07 ± 0.65 mm (-0.37 ± 0.52 mm; p = 0.001).Mean canal diameter did not change significantly at either adjacent level.Lower adjacent disc height decreased from 7.03 ± 1.36 to 6.55 ± 1.09 mm (-0.48 ± 0.73 mm; p = 0.003).These changes remained significant after Holm adjustment.Neither global C2-7 alignment nor the index segmental angle changed significantly at the cohort level.None of the hypothesis-generating exploratory correlations remained significant after FDR correction.Conclusion: Single-level ACDF substantially expanded the index-level spinal canal and reduced LF thickness at that level.Lower adjacent disc height also decreased measurably.These findings support evaluating postoperative adjacent-segment behavior using a multiscale radiological framework that distinguishes global alignment, regional segmental correction, and local MRI morphology.