A Nationwide Registry Study Comparing Long-term Risk of Adjacent Segment Disease Requiring Reoperation Following Anterior Cervical Discectomy and Fusion Versus Cervical Disc Arthroplasty.

OBJECTIVE: Adjacent segment disease (ASD) is a recognized long-term complication after anterior cervical discectomy and fusion (ACDF). Cervical disc arthroplasty (CDA) was introduced as a motion-preserving alternative, thought to reduce stress at adjacent levels and lower ASD risk. This study aimed to compare the risk of ASD requiring reoperation after ACDF and CDA and identify factors associated with ASD. METHODS: This retrospective cohort study used prospectively collected data from the Swedish Spine Registry (Swespine) and included adult patients undergoing anterior cervical surgery for degenerative cervical disease between 2006 and 2026. ASD was defined as a secondary operation at an adjacent level ≥12 months after the index procedure. Cumulative incidence was estimated using Kaplan-Meier analysis, and associations with ASD were evaluated using multivariable Cox proportional hazards regression. Radiological or conservatively treated ASD were not assessed. RESULTS: A total of 9,338 patients were included (ACDF, n=9,005; CDA, n=333). During 45,666 person-years follow-up, 509 ASD events occurred (incidence rate 11.1 per 1,000 person-years). Cumulative incidence was 4.9% at 5 years and 10.4% at 10 years. CDA was associated with lower ASD hazard than ACDF (hazard ratio [HR], 0.61) though this association was not significant after propensity score matching (HR, 0.88). Multilevel procedures (HR, 0.61), increasing age (HR, 0.96 per year), and radiculopathy were associated with lower risk, while myelopathy or stenosis was associated with higher risk (HR, 1.22). CONCLUSION: The long-term risk of ASD requiring reoperation was lower than previously reported. After adjustment, CDA was associated with lower ASD risk compared to ACDF, although the absolute difference was small, and the clinical significance remains uncertain.