• Masanori Izeki, Masashi Neo, Hiromu Ito, Koutatsu Nagai, Tatsuro Ishizaki, Takeshi Okamoto, Shunsuke Fujibayashi, Mitsuru Takemoto, Hiroyuki Yoshitomi, Tomoki Aoyama, and Shuichi Matsuda.
• *Department of Orthopaedic Surgery †Department of the Control for Rheumatic Diseases, and ‡Department of Human Health Science, Graduate School of Medicine, Kyoto University, Japan §Department of Orthopaedic Surgery, Osaka Medical College, Japan ¶Faculty of Health Science, Department of Physical Therapy, Kyoto Tachibana University, Japan; and ‖Human Care Research Team, Tokyo Metropolitan Institute of Gerontology, Tokyo, Japan.
• Spine. 2013 Apr 20; 38 (9): E513-20.

Study DesignA cross-sectional study.ObjectiveThe purpose of this study was to investigate the effect of reduction of anterior atlantoaxial subluxation (AAS) on the oropharyngeal airway space.Summary Of Background DataOur previous studies have shown that reduction of the occipito-C2 angle (O-C2A) makes the mandible shift posteriorly, resulting in oropharyngeal airway stenosis, which occasionally causes postoperative dysphagia after occipitocervical fusion. Based on this background, we hypothesized that reduction of AAS would also cause oropharyngeal airway stenosis independent of the O-C2A, because it also shifts the mandible posteriorly. To our knowledge, there are no data demonstrating an association between reduction of AAS and the oropharyngeal airway space.MethodsThe authors prospectively evaluated 64 patients with rheumatoid arthritis. We analyzed lateral cervical plain radiographs of 5 different positions (neutral, flexion, extension, retraction, and protrusion), and measured the O-C2A, C2-C6 angle, anterior atlantodental interval, anteroposterior distance of the narrowest oropharyngeal airway space (nPAS), and so on. The subjects were classified into 2 groups: group R comprised patients with a "reducible AAS" in dynamic cervical movement, and group N comprised "patients without AAS" patients.ResultsIn the multiple regression analysis, the change in the O-C2A was the only significant independent variable related to the percentage change in the nPAS from the neutral position in group N. On the contrary, the change in the anterior atlantodental interval and change in the O-C2A were significantly related to the percentage change in the nPAS in group R. No cases in group N and 7 cases (28%) in group R showed a paradoxical decrease in the nPAS in extension, in which the O-C2A is largest and reduction of AAS is obtained.ConclusionReduction of AAS has a negative effect on the oropharyngeal airway space. Therefore, reduction of AAS during occipitocervical fusion may cause postoperative dysphagia despite maintenance of the O-C2A.

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