title: Impact of the O-C2 angle on the oropharyngeal space in normal patients.
abstract: METHODS
  Radiographic analysis using normal patients.
  
  
  OBJECTIVE
  To analyze the relationship between the cervical alignment and the oropharyngeal space.
  
  
  BACKGROUND
  Few 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.
  
  
  METHODS
  Plain 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.
  
  
  RESULTS
  According 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.
  
  
  CONCLUSIONS
  Our 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.
authors.affiliation: Department of Orthopaedic Surgery, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Masato
authors.initials: M
authors.lastname: Ota
authors.forename: Masashi
authors.initials: M
authors.lastname: Neo
authors.forename: Tomoki
authors.initials: T
authors.lastname: Aoyama
authors.forename: Tatsuro
authors.initials: T
authors.lastname: Ishizaki
authors.forename: Shunsuke
authors.initials: S
authors.lastname: Fujibayashi
authors.forename: Mitsuru
authors.initials: M
authors.lastname: Takemoto
authors.forename: Takeo
authors.initials: T
authors.lastname: Nakayama
authors.forename: Takashi
authors.initials: T
authors.lastname: Nakamura
mesh_terms: D000328:Adult; D001268:Atlanto-Axial Joint / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000601:surgery; D001269:Atlanto-Occipital Joint / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000601:surgery; D001368:Axis, Cervical Vertebra / Q000033:anatomy & histology / Q000000981:diagnostic imaging* / Q000502:physiology*; D016022:Case-Control Studies; D005260:Female; D019416:Head Movements / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009777:Occipital Bone / Q000033:anatomy & histology / Q000000981:diagnostic imaging* / Q000502:physiology*; D009960:Oropharynx / Q000033:anatomy & histology / Q000000981:diagnostic imaging* / Q000502:physiology*; D011183:Postoperative Complications / Q000175:diagnosis / Q000473:pathology; D011859:Radiography; D016059:Range of Motion, Articular / Q000502:physiology; D012016:Reference Values; D013123:Spinal Fusion / Q000009:adverse effects / Q000379:methods; D055815:Young Adult