How Subsidence Affects Clinical and Radiological Outcomes after Stand-Alone Anterior Cervical Discectomy and Fusion on Patients with Degenerative Cervical Disease? A Long-Term Follow-Up Study

Objective: We aimed to examine the long-term radiological and clinical outcomes after stand-alone anterior cervical discectomy and fusion (ACDF).Methods: In total, we enrolled 20 patients and 31 treated segments with degenerative cervical disease that underwent stand-alone ACDF with ≥60 months of follow-up. Segmental angle (SA), cervical sagittal alignment (CSA), subsidence, and fusion were evaluated. A visual analogue scale (VAS) and the neck disability index (NDI) were applied pre- and post-operatively and at the last follow-up.Results: Subsidence occurred in 9 (45%) patients and 15 segments (48.4%) at the last follow-up. The mean VAS and NDI scores had improved in both groups with and without subsidence. The mean SA at the last follow-up had significantly increased to 2.3°±8.5° in the subsidence group and to 1.7°± 5.2° degree in the non-subsidence group compared to the post-operative SA (p<0.001). The overall mean CSA at the last follow-up significantly increased overtime in both groups from the postoperative CSA (p=0.003). The fusion rate was 86.7% in the subsidence group and 81.3% in non-subsidence group. However, the difference in SA, CSA and fusion rates between the two groups were not statistically significant (p=0.119, 0.98, and 0.682, respectively).Conclusion: As a result of a long-term follow-up study after stand-alone ACDF, subsidence occurs to some extent. Still, it does not appear to significantly impact radiological and clinical outcomes if the clinician performs sufficient decompression of foramen during surgery. Subsidence seems to have a positive influence on the fusion rate.