• Masato Ota, Masashi Neo, Tomoki Aoyama, Tatsuro Ishizaki, Shunsuke Fujibayashi, Mitsuru Takemoto, Takeo Nakayama, and Takashi Nakamura.
• Department of Orthopaedic Surgery, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
• Spine. 2011 May 15;36(11):E720-6.

Study DesignRadiographic analysis using normal patients.ObjectiveTo analyze the relationship between the cervical alignment and the oropharyngeal space.Summary Of Background DataFew clinical studies stress the effect of the occipito-C2 (O-C2) alignment on the oropharyngeal space. A previous study showed dysphagia and/or dyspnea after occipitocervical fusion was caused by oropharyngeal stenosis resulting from O-C2 fixation in a flexed position. Other independent researchers showed that development or improvement of obstructive sleep apnea in rheumatoid arthritis patients was related to the O-C2 alignment. However, there are limited basic data demonstrating the relationship between the O-C2 alignment and the oropharyngeal space.MethodsPlain lateral cervical radiographs in five tested positions--neutral, flexion, extension, protrusion, and retraction--of 40 asymptomatic volunteers were collected. The O-C2 angle, the C2-C6 angle, and the anterior-posterior distance of the narrowest oropharyngeal airway space (nPAS) were measured, and the changes in value from the neutral to the other four positions were calculated for each patient.ResultsAccording to the multiple regression analysis, there was an extremely strong linear correlation of the change in the O-C2 angle with the percentage change in the nPAS. Referring to the multiple regression analysis, a decrease of 10° in the O-C2 angle caused a 37% reduction in the nPAS in the neutral position. In contrast, no significant correlation was found between the change in the C2-C6 angle and the percentage change in the nPAS.ConclusionOur results show the impact of the O-C2 angle on the oropharyngeal space. This knowledge will be useful for the diagnosis and treatment of the upper cervical lesion combined with the upper airway stenosis, and for the determination of the optimal fixation angle in occipitocervical fusion.

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