title: Relation between alignments of upper and subaxial cervical spine: a radiological study.
abstract: OBJECTIVE
  To reveal the relation between alignments of upper and subaxial cervical spine and deduce the optimal atlantoaxial fusion angle by a radiological study.
  
  
  METHODS
  414 asymptomatic volunteers (213 males, 201 females) underwent cervical lateral radiographs in neutral position. The Oc-C2 angle, C1-C2 angle and C2-C7 angle were measured. Relations among these three angles and relations between angles and age were analyzed.
  
  
  RESULTS
  The mean Oc-C2 angle was 16.3° ± 7.0° in females, significantly larger than 14.9° ± 6.5° in males. The mean C1-C2 angles were 28.2° ± 4.0° in females and 26.4° ± 4.6° in males, and C2-C7 angles were 12.7° ± 6.6° and 16.3° ± 7.3°, correspondingly. The mean C1-C2 angle in females was significantly larger than that in males, while C2-C7 angle smaller than that in males. The C2-C7 angle correlated significantly not only with C1-C2 angle but also with Oc-C2 angle. And correlation between C1-C2 angle and C2-C7 angle was stronger than that between Oc-C2 angle and C2-C7 angle. There were also significant positive correlations between C1-C2 and Oc-C2 angles. Oc-C2 angle, C1-C2 angle, and C2-C7 angle correlated significantly with age in both sexes.
  
  
  CONCLUSIONS
  There were negative correlations between C1-C2 angle and C2-C7 angle as well as between Oc-C2 angle and C2-C7 angle, and the former correlation was stronger. C1-C2 fixation angle was the key to regulate postoperative subaxial alignment in atlantoaxial arthrodesis. The optimal atlantoaxial fusion angle may be between 25° and 30°.
authors.affiliation: Department of Orthopedics, Changzheng Hospital, The Second Military Medical University, 415 Fengyang Road, Huangpu District, Shanghai 200003, People's Republic of China.
authors.forename: Qunfeng
authors.initials: Q
authors.lastname: Guo
authors.forename: Bin
authors.initials: B
authors.lastname: Ni
authors.forename: Jian
authors.initials: J
authors.lastname: Yang
authors.forename: Kai
authors.initials: K
authors.lastname: Liu
authors.forename: Zhichao
authors.initials: Z
authors.lastname: Sun
authors.forename: Fengjin
authors.initials: F
authors.lastname: Zhou
authors.forename: Jianxin
authors.initials: J
authors.lastname: Zhang
mesh_terms: D000328:Adult; D000368:Aged; D001268:Atlanto-Axial Joint / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D002574:Cervical Vertebrae / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011859:Radiography