title: A retrospective radiographic analysis of subaxial sagittal alignment after posterior C1-C2 fusion.
abstract: METHODS
  Subaxial sagittal alignment following atlantoaxial (A-A) posterior fusion was investigated retrospectively in patients with A-A subluxation.
  
  
  OBJECTIVE
  To evaluate the association between A-A fusion angle and postoperative subaxial sagittal alignment and to determine the optimal fusion angle for preservation of physiologic subaxial alignment.
  
  
  BACKGROUND
  A-A posterior fusion has been used for patients with A-A instability and provided satisfactory clinical results. However, there are patients showing unexpected development of subaxial kyphosis after surgery. The reasons for subaxial kyphosis after A-A fusion remain unclear.
  
  
  METHODS
  Seventy-six patients with A-A subluxation who underwent several types of posterior A-A fusion were involved. There were 46 women and 30 men. The causes of A-A subluxation were rheumatoid arthritis in 47, trauma in 16, os odontoideum in 8, and unknown in 5. The methods of posterior fusion consisted of Magerl procedure with posterior wiring in 51, Brooks wiring in 18, and Halifax clamp in 7. Angles at C1-C2, C2-C7, and C1-C7 in the neural position were measured before surgery and at the final follow-up to find out any association between postoperative C2-C7 angle and the other radiologic parameters. The association between O-C1 range of motion and C2-C7 angle was also investigated.
  
  
  RESULTS
  The mean angles of C1-C2, C2-C7, and C1-C7 before surgery were 18.4 degrees, 14.5 degrees, and 32.9 degrees, respectively. Those at the final follow-up were 26.0 degrees, 5.5 degrees, and 31.5 degrees, respectively. These results indicated that C1-C2 fixation in a hyperlordotic position led to a subaxial kyphosis after surgery. Statistics showed that there was a linear association between the C1-C2 lordotic fixation angle and the C2-C7 kyphotic angle.
  
  
  CONCLUSIONS
  Surgical fixation of A-A joint in a hyperlordotic position will lead the lower cervical spine to a kyphotic sagittal alignment after surgery. To maintain the physiologic sagittal alignment of the subaxial cervical spine, C1-C2 should not be fixed in a hyperlordotic position.
authors.affiliation: Department of Orthopaedic Surgery, Hokkaido University Gradate School of Medicine, Sapporo, Japan.
authors.forename: Hisashi
authors.initials: H
authors.lastname: Yoshimoto
authors.forename: Manabu
authors.initials: M
authors.lastname: Ito
authors.forename: Kuniyoshi
authors.initials: K
authors.lastname: Abumi
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Kotani
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Shono
authors.forename: Takashige
authors.initials: T
authors.lastname: Takada
authors.forename: Akio
authors.initials: A
authors.lastname: Minami
mesh_terms: D001268:Atlanto-Axial Joint / Q000000981:diagnostic imaging / Q000601:surgery; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging* / Q000601:surgery*; D018450:Disease Progression; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007738:Kyphosis / Q000000981:diagnostic imaging / Q000209:etiology; D008141:Lordosis / Q000000981:diagnostic imaging / Q000209:etiology; D008297:Male; D009333:Neck / Q000000981:diagnostic imaging; D019547:Neck Pain / Q000209:etiology; D011859:Radiography; D016059:Range of Motion, Articular; D012189:Retrospective Studies; D013123:Spinal Fusion / Q000009:adverse effects; D016896:Treatment Outcome