Risk Factors of Subsidence after Anterior Cervical Discectomy and Fusion with Double Cylindrical Cages for Cervical Degenerative Diseases: Minimum Two-year Follow-up Results

Cylindrical cages were known to cause subsidence after anterior cervical discectomy and fusion (ACDF); hence, they were gradually replaced by box-shaped cages. However, this phenomenon has been inconclusive due to limited information and short-term results. Therefore, this study aimed to clarify risk factors for subsidence after ACDF using titanium double cylindrical cages with mid-term follow-up periods. This retrospective study included 49 patients (76 segments) diagnosed with cervical radiculopathy or myelopathy caused by disc herniation, spondylosis, and ossification of the posterior longitudinal ligament. These patients underwent ACDF using these cages from January 2016 to March 2020 in a single institution. Patient demographics and neurological outcomes were also examined. Subsidence was defined as a ≥3-mm segmental disc height decrease at the final follow-up lateral X-ray compared to that on the next day postoperatively. Subsidence occurred in 26 of 76 segments (34.7%) within the follow-up periods of approximately three years. Multivariate analysis using a logistic regression model demonstrated that multilevel surgery was significantly associated with subsidence. The majority of patients achieved good clinical outcomes based on the Odom criteria. This study demonstrated that multilevel surgery was the only risk factor of subsidence post-ACDF with double cylindrical cages. Despite the relatively high subsidence rates, the clinical outcome was almost good at least during the mid-term period.