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.

Figure 1

Illustration (A) and MRI scan (B) showing the central anterior to posterior (A-P) measurement of the zygapophysial (Z) joints that were made from the left and right L4/L5 and L5/S1 Z joints in this study.

Figure 1

Illustration (A) and MRI scan (B) showing the central anterior to posterior (A-P) measurement of the zygapophysial (Z) joints that were made from the left and right L4/L5 and L5/S1 Z joints in this study.

Figure 2

Bland and Altman (1986) plots showing the differences (Y axis) between Measurement 1 and Measurement 2 (separated by a minimum of 4 weeks) plotted against the averages (X axis) of the same two measurements. The plots include the values of Observers 1-3 (A-C) and the values of all three observers to assess overall agreement (Fig. 2D).