title: Reliability of zygapophysial joint space measurements made from magnetic resonance imaging scans of acute low back pain subjects: comparison of 2 statistical methods.
abstract: OBJECTIVE
  This purpose of this study was to assess the reliability of measurements made of the zygapophysial (Z) joint space from the magnetic resonance imaging scans of subjects with acute low back pain using new equipment and 2 different methods of statistical analysis. If found to be reliable, the methods of Z joint measurement can be applied to scans taken before and after spinal manipulation in a larger study of acute low back pain subjects.
  
  
  METHODS
  Three observers measured the central anterior-to-posterior distance of the left and right L4/L5 and L5/S1 Z joint space from 5 subject scans (20 digitizer measurements, rounded to 0.1 mm) on 2 separate occasions separated by 4 weeks. Observers were blinded to each other and their previous work. Intra- and interobserver reliability was calculated by means of intraclass correlation coefficients and also by mean differences using the methods of Bland and Altman (1986). A mean difference of less than +/-0.4 mm was considered clinically acceptable.
  
  
  RESULTS
  Intraclass correlation coefficients showed intraobserver reliabilities of 0.95 (95% confidence interval, 0.87-0.98), 0.83 (0.62-0.92), and 0.92 (0.83-0.96) for each of the 3 observers and interobserver reliabilities of 0.90 (0.82-0.95), 0.79 (0.61-0.90), and 0.84 (0.75-0.90) for the first and second measurements and overall reliability, respectively. The mean difference between the first and second measurements was -0.04 mm (+/-1.96 SD = -0.37 to 0.29), 0.23 (-0.48 to 0.94), 0.25 (-0.24 to 0.75), and 0.15 (-0.44 to 0.74) for each of the 3 observers and the overall agreement, respectively.
  
  
  CONCLUSIONS
  Both statistical methods were found to be useful and complementary and showed the measurements to be highly reliable.
authors.affiliation: Department of Research, National University of Health Sciences, Lombard, IL 60510, USA. gcramer@nuhs.edu
authors.forename: Gregory D
authors.initials: GD
authors.lastname: Cramer
authors.forename: Joe A
authors.initials: JA
authors.lastname: Cantu
authors.forename: Judith D
authors.initials: JD
authors.lastname: Pocius
authors.forename: Jerrilyn A
authors.initials: JA
authors.lastname: Cambron
authors.forename: Ray A
authors.initials: RA
authors.lastname: McKinnis
mesh_terms: D000208:Acute Disease; D002684:Chiropractic / Q000379:methods* / Q000706:statistics & numerical data*; D006801:Humans; D007596:Joints / Q000473:pathology*; D017116:Low Back Pain / Q000473:pathology* / Q000534:rehabilitation*; D008159:Lumbar Vertebrae / Q000473:pathology; D008279:Magnetic Resonance Imaging; D011187:Posture; D015203:Reproducibility of Results; D012399:Rotation