title: Risk factors for development of subaxial subluxations following atlantoaxial arthrodesis for atlantoaxial subluxations in rheumatoid arthritis.
abstract: METHODS
  Retrospective radiographic/imaging study.
  
  
  OBJECTIVE
  To evaluate preoperative and sequential postoperative radiographs following C1-C2 arthrodesis for atlantoaxial subluxation in patients with rheumatoid arthritis (RA) to determine risk factors for the development of subaxial subluxations (SAS).
  
  
  BACKGROUND
  The development of SAS has often been observed after C1-C2 arthrodesis. However, there have been no previous reports on the correlation between radiographic parameters and the incidence of postoperative SAS.
  
  
  METHODS
  The study group comprised of 58 patients with RA who underwent C1-C2 arthrodesis due to atlantoaxial subluxation. There were 5 men and 53 women with a mean age of 55.8 years. The mean follow-up period was 137 months. Nineteen patients with a postoperative SAS after C1-C2 arthrodesis were classified as the SAS+ group. Other 39 patients without a postoperative SAS were included in the SAS- group. Clinical outcomes and plain radiographs were reviewed retrospectively and compared between the 2 groups.
  
  
  RESULTS
  The difference between pre- and postoperative atlantoaxial (AA) angles in the SAS+ group was significantly greater than those in the SAS- group (P = 0.039). The C2-C7 angles changed significantly between pre- and postoperative periods in the SAS+ group (P = 0.039), but not in the SAS- group (P = 0.897). It was suggested that a large AA angle and a small C2-C7 angle observed at the early postoperative period were the risk factors for the development of SAS. We also demonstrated that a high incidence of the C3-C4 SAS resulted from excessive bone fusion at the C2-C3.
  
  
  CONCLUSIONS
  Excessive correction of AA angle is likely to cause loss of cervical lordosis, resulting in the development of postoperative SAS. In addition, extensive bony union at C2-C3 following C1-C2 arthrodesis frequently leads to the development of extensive SAS at the C3-C4.
authors.affiliation: Department of Orthopaedic Surgery, School of Medicine, Keio University, Shinjuku, Tokyo, Japan.
authors.forename: Ken
authors.initials: K
authors.lastname: Ishii
authors.forename: Morio
authors.initials: M
authors.lastname: Matsumoto
authors.forename: Yuichiro
authors.initials: Y
authors.lastname: Takahashi
authors.forename: Eijiro
authors.initials: E
authors.lastname: Okada
authors.forename: Kota
authors.initials: K
authors.lastname: Watanabe
authors.forename: Takashi
authors.initials: T
authors.lastname: Tsuji
authors.forename: Hironari
authors.initials: H
authors.lastname: Takaishi
authors.forename: Masaya
authors.initials: M
authors.lastname: Nakamura
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Toyama
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Chiba
mesh_terms: D000328:Adult; D000368:Aged; D001172:Arthritis, Rheumatoid / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D001268:Atlanto-Axial Joint / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D001270:Cervical Atlas / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery; D002574:Cervical Vertebrae / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D018450:Disease Progression; D005260:Female; D006801:Humans; D004204:Joint Dislocations / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D007593:Joint Instability / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D011183:Postoperative Complications / Q000000981:diagnostic imaging / Q000209:etiology* / Q000473:pathology; D011859:Radiography; D012189:Retrospective Studies; D012307:Risk Factors; D013121:Spinal Curvatures / Q000000981:diagnostic imaging / Q000209:etiology / Q000473:pathology; D013123:Spinal Fusion / Q000009:adverse effects / Q000379:methods; D055815:Young Adult