Study Design: This is a prospective study. Objective: The purpose of this study was to analyze the factors influencing subsidence following anterior cervical discectomy and fusion (ACDF) using a stand-alone cage. Summary of Background Data: The relationship between cage subsidence and cage height and material has been reported in previous studies. Methods: Clinical and radiologic data from 78 patients, 105 levels, undergoing single-level and 2-level ACDF without plates from 2007 to 2015 were collected prospectively. Patients were followed for at least 12 months after surgery. Radiographs were obtained preoperatively, at 1 week, and at 1, 3, 6, and 12 months postoperatively to determine the presence of fusion and cage subsidence. Results: There was a correlation in cage height and subsidence (Spearman P<0.05). Cage subsidence was significantly shorter in the polyetheretherketone cages than in titanium cages (P<0.05). However, when cage height was <5 mm, the difference between the 2 groups was not significant. Large subsidence (>3 mm) was observed in 17 patients, 20 levels, many of whom exhibited sinking in the first month after surgery. Conclusions: The greater the cage height, the greater the risk of cage subsidence in ACDF. Polyetheretherketone cages are superior to titanium cages for the maintenance of intervertebral height in cases where cage height is >5.5 mm. Level of Evidence: Level 3.

Patients with preoperative sagittal imbalance have a statistically significant increased risk of ASD. The risk of ASD incidence was 5.1 times greater in subjects with preoperative PT of more than 22.5°.

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