Risk Factors of Cage Subsidence in Patients with Ossification of Posterior Longitudinal Ligament (OPLL) After Anterior Cervical Discectomy and Fusion.

BACKGROUND There are numerous reports on cage subsidence after ACDF; however, few studies have identified its risk factors. The current study aimed to identify risk factors for cage subsidence after ACDF using the PEEK cage packed with local autobone implant with plate and provides evidence for surgical decision-making. MATERIAL AND METHODS We retrospectively reviewed 77 patients with OPLL who underwent 1/2-level ACDF using the PEEK cage packed with local autobone implant with plate from March 2013 to December 2015. Implant subsidence was defined as the decrease in interbody height at the final follow-up compared to that measured on the first postoperative day ≥2 mm. Intervertebral fusion was evaluated on the basis of no motion across the fusion site and the presence of trabeculae between bone and implant in the X-rays. Multivariate logistic regression analysis was used to identify the risk factors for cage subsidence. RESULTS In comparing the end-plate removal group with the end-plate preservation group, we found that the fusion rate (removal group, 35.90%; preservation group, 10.50%) and the change of IH (P=0.011) were significantly different during the first 6 weeks after surgery. Advanced age (OR=1.34, 95% CI=1.04-1.24, P=0.004), end-plate removal (OR=11.84, 95% CI=2.91-48.28, P=0.001), and nonunion within 6 weeks after surgery (OR=22.67, 95% CI=2.36-217.67, P=0.007) played an important role in predicting cage subsidence. CONCLUSIONS These findings suggest that advanced age, end-plate removal, and nonunion within 6 weeks after surgery are risk factors for the cage subsidence after ACDF using the PEEK cage packed with local autobone implant with plate in patients with OPLL.