title: CT analysis of the axis for transarticular screw fixation of rheumatoid atlantoaxial instability.
abstract: OBJECTIVE
  To investigate the morphological characteristics of the axis of rheumatoid arthritis (RA) patients with atlantoaxial instability and to determine, by means of sagittal reconstructed computed tomography (CT), the suitability for atlantoaxial transarticular screw fixation.
  
  
  METHODS
  Twenty-seven patients, who had undergone reconstructed cervical spine CT scanning preoperatively and posterior atlantoaxial arthrodesis for atlantoaxial instability, were identified from a database for inclusion in this study. The isthmus height and internal height of the lateral mass of the axis were measured using digital imaging software.
  
  
  RESULTS
  The mean isthmus height and internal height of the lateral mass of the axis in RA patients (n=14) were significantly lower than in non-RA patients (n=13) (P<0.01). A high-riding vertebral artery (VA) was present in 54% (15 joints, 9 patients) of the 28 atlantoaxial joints in the RA group and in 12% (3 joints, 2 patients) of the 26 atlantoaxial joints in the non-RA group (P<0.01).
  
  
  CONCLUSIONS
  In RA patients, the axis showed more extensive thinning of the isthmus and lateral mass than in non-RA patients. A precise preoperative evaluation of screw trajectory using reconstruction CT imaging may be useful in atlantoaxial transarticular fixation, particularly for RA patients with atlantoaxial instability.
authors.affiliation: Department of Orthopedic Surgery, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, 135-710, South Korea.
authors.forename: Sung Soo
authors.initials: SS
authors.lastname: Chung
authors.forename: Chong Suh
authors.initials: CS
authors.lastname: Lee
authors.forename: Hye Won
authors.initials: HW
authors.lastname: Chung
authors.forename: Chang Seok
authors.initials: CS
authors.lastname: Kang
mesh_terms: D001172:Arthritis, Rheumatoid / Q000000981:diagnostic imaging* / Q000601:surgery*; D001268:Atlanto-Axial Joint / Q000000981:diagnostic imaging* / Q000601:surgery*; D001863:Bone Screws; D016009:Chi-Square Distribution; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000000981:diagnostic imaging* / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D011857:Radiographic Image Interpretation, Computer-Assisted; D018709:Statistics, Nonparametric; D014057:Tomography, X-Ray Computed