Radiographic subsidence after single-level anterior cervical discectomy and fusion; a comparison between blade-anchored zero-profile cages and stand-alone cages

BACKGROUND: Cage subsidence is a common radiographic finding after anterior cervical discectomy and fusion (ACDF), particularly with stand-alone cages, and may compromise postoperative alignment and stability. Blade-anchored zero-profile cages have been developed to provide immediate fixation while avoiding plate-related complications; however, their influence on subsidence characteristics has not been fully elucidated. This study aimed to compare the magnitude and direction of radiographic subsidence between blade-anchored zero-profile cages and stand-alone cages after single-level ACDF. METHODS: This retrospective single-center study included 76 patients who underwent single-level ACDF between 2017 and 2024 using either a blade-anchored zero-profile cage or a stand-alone cage. The anterior disc height (ADH) and posterior disc height (PDH) were measured preoperatively, immediately postoperatively, and at 6 months after surgery. The mean disc height was defined as the average of the ADH and PDH. Radiographic subsidence was calculated as the difference between the immediate postoperative and 6-month mean disc heights. Anterior and posterior subsidence were analyzed separately. Multivariable linear regression analyses were performed in two steps: Model 1 adjusted for demographic and baseline radiographic variables, and Model 2 further adjusted for disc height recovery to account for the effect of intraoperative disc height restoration. RESULTS: Mean subsidence was significantly greater in the blade-anchored zero-profile cage group than in the stand-alone cage group, and the incidence of subsidence ≥ 3 mm was higher with blade-anchored cages. Directional analysis demonstrated significantly greater anterior subsidence in the blade-anchored group, whereas posterior subsidence did not differ between the groups. In the multivariate analysis, cage type was independently associated with subsidence in Model 1; however, this association was attenuated after adjustment for disc height recovery in Model 2. CONCLUSIONS: Blade-anchored zero-profile cages were associated with greater radiographic subsidence after single-level ACDF compared with stand-alone cages, primarily due to increased anterior subsidence. The attenuation of the cage-type effect after adjustment for disc height recovery suggests a potential role of restoration-related factors. Directional assessment of subsidence may provide additional insights into implant-specific behavior.