Impact of the occiput and external acoustic meatus to axis angle on dysphagia in patients suffering from anterior atlantoaxial subluxation after occipitocervical fusion

BACKGROUND CONTEXT: Dysphagia is a complication that sometimes occurs after fusion (OCF). An appropriate O-C2 angle (O-C2a) is recognized as a critical factor for preventing dysphagia. The occiput and external acoustic meatus to axis angle (O-EAa) has some advantages over the O-C2a and is now recognized to outperform O-C2a in predicting dysphagia. However, there are no data on this topic from patients with anterior atlantoaxial subluxation (AAS). PURPOSE: To evaluate the relationship between the O-EAa and dysphagia in patients suffering from AAS after OCF surgery. STUDY DESIGN: A retrospective clinical study. PATIENT SAMPLE: Data from 22 consecutive AAS patients who had undergone OCF were reviewed retrospectively. OUTCOME MEASURES: The outcome measures included the O-EAa, O-C2a, the narrowest oropharyngeal airway space (nPAS), and the morbidity of dysphagia after OCF. METHODS: Between September 2011 and September 2017, data from 22 consecutive AAS patients who had undergone OCF were reviewed retrospectively. The patients were divided into two groups according to whether they had suffered postoperative dysphagia by face-to-face questioning or telephone interview. Lateral radiographs were analyzed to determine the pre- and postoperative O-EAa, O-C2a, angle formed by the inferior endplate of C2 and the EA-line (C2Ta), and smallest anteroposterior diameter of the oropharynx between the levels of the uvula and the tip of the epiglottis (nPAS). RESULTS: The incidence of dysphagia after OCF was 18.18% (4/22). The pre- and postoperative mean nPAS values were significantly different between the groups (p<.05). The postoperative mean O-EAa of the group with dysphagia was significantly smaller than that of the group without dysphagia (p<.05). The mean change in nPAS was significantly larger in the group with dysphagia than that in the group without dysphagia (p<.05). The changes in the O-EAa, O-C2a, and nPAS were linearly correlated within patients. The marginal R-2 values for the patients were 0.452 and 0.202 for the O-EAa and O-C2a, respectively. CONCLUSIONS: The O-EAa impacts dysphagia in patients with AAS after OCF. Measuring this angle intraoperatively may be a simple and effective procedure. The O-EAa may be used as a practical index to avoid postoperative dysphagia in patients with AAS after OCF. (C) 2019 Elsevier Inc. All rights reserved.