Purpose: Adjacent segment degeneration (ASD) is known to occur after anterior cervical arthrodesis. However, it is not known whether cervical canal stenosis enhances the risk of ASD. The purpose of this study was to explore whether congenital stenosis could be used as a predictor of ASD after anterior cervical decompression and fusion (ACDF).
Methods: We enrolled 141 patients who had undergone ACDF for cervical myelopathy and/or radiculopathy, and had at least 6 years of follow-up. In standard radiographs of cervical spine in lateral view, bony congenital stenosis was evaluated and all patients were divided into two groups: stenosis (n = 63) and non-stenosis (n = 78). Radiographic ASD was assessed according to the criteria of Kellgren and Lawrence and correlated with symptomatic ASD. Clinical and radiological parameters were compared between the groups. The primary outcome was the rate of radiographic ASD after initial ACDF. The incidence of symptomatic ASD was assessed by Kaplan-Meier method.
Results: Radiographic ASD and symptomatic ASD developed in 46.8 % and 18.4 % of all patients, respectively. There was a significant association between congenital stenosis and radiographic ASD. The area under the receiver operating characteristic curve of preoperative anteroposterior (AP) diameter of cervical canal for predicting radiographic ASD was 0.756. 13.0 mm was the cutoff value of preoperative AP diameter of cervical canal predicting radiographic ASD. Kaplan-Meier analysis predicted a disease-free survival rate of symptomatic ASD in 97.2 % of patients at 5 years and 78.0 % at 10 years after ACDF. There was no significant difference in survival rates of the adjacent segment between the two groups via log-rank analysis (P = 0.102).
Conclusion: Congenital stenosis can increase the rate of radiographic ASD after initial ACDF. The cutoff value of 13.0 mm for preoperative AP diameter of cervical canal had the highest validity for predicting radiographic ASD.