Risk factors for postoperative subsidence of single-level anterior cervical discectomy and fusion: the significance of the preoperative cervical alignment.

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Retrospective cohort study. To investigate and analyze the preoperative risk factors affecting subsidence after anterior cervical discectomy and fusion (ACDF) to reduce subsidence. Subsidence after ACDF may be caused by various risk factors, although the related information is scarce. Seventy-eight patients who underwent single-level ACDF between 2005 and 2011 were included. Patients were categorized into the subsidence (n = 26) and nonsubsidence groups (n = 52). Preoperative factors such as age, sex, operative level, bone mineral density, cervical alignment, segmental sagittal angle, and anterior/posterior disc height were assessed. The use of plates and the anterior/posterior disc height gap were examined as perioperative factors. The clinical outcome was assessed using a visual analogue scale for neck and arm pain. Subsidence occurred in 26 (33.3%) of 78 patients. A significant difference was found in clinical outcomes between the subsidence and nonsubsidence groups (P < 0.05). The fusion rate was 61.5% in the subsidence group. The mean time to subsidence was 4.8 months. Logistic regression analysis revealed that cervical alignment (P = 0.017), age (P = 0.022), and use of plates (P = 0.041) affected subsidence. In patients who received a stand-alone cage, the risk of subsidence was significantly greater in the kyphotic angle group than in the lordotic angle group (odds ratio = 13.56; P < 0.001). After ACDF, the main factors affecting subsidence are cervical alignment, age, and use of plates. Our data suggest that surgeons should consider the kyphotic curvature and/or age when deciding on the use of plates.