Mylène Jansen

220 Chapter 11 All bone densities (Figure 2A and S1), eminence height (Figure S4), and joint angle (Figure S5) plots did not show any large systematic differences between the 2 readings. However, the minimum JSW (Figure 2B and S2) and osteophyte plots (Figure 2C and S3) showed a floor effect, where measurements resulted in 0 in 1 analysis, but not in the other (as indicated by the straight line of dots starting from around 0). Figure 2 : Bland-Altman plots for all 293 available radiographs that were analyzed twice, for (A) the bone density of the medial tibia in mm aluminum equivalent (mm Al eq), (B) the minimum joint space width in mm and (C) the osteophyte area of the lateral femur in mm 2 . The ICC, mean and SD of all measurements, mean of the differences between 2 analysis moments, SD and 95%CI of the difference, and the SDD are shown in Table 1. Table 1 : Intra-observer results for all severe radiographs reanalyzed within a large period of time Mean (SD) Mean Δ SD Δ 95%CI Δ SDD ICC Bone density (all in mm Al eq) Femur mean lateral 33.0 (4.6) -0.05 0.31 -0.09 to -0.02 0.61 0.998 Femur mean medial 37.3 (5.1) 0.17 0.33 0.13 to 0.21 0.65 0.997 Tibia mean lateral 33.7 (5.2) -0.59 1.41 -0.75 to -0.43 2.76 0.958 Tibia mean medial 38.6 (5.0) 0.32 0.50 0.26 to 0.38 0.98 0.993 JSW (all in mm) Mean 5.2 (1.1) 0.37 0.59 0.30 to 0.44 1.16 0.821 Mean lateral 7.7 (1.9) 0.66 1.03 0.54 to 0.77 2.02 0.816 Mean medial 2.7 (1.7) 0.09 0.39 0.04 to 0.13 0.76 0.973 Minimum 1.0 (1.1) -0.18 0.45 -0.23 to -0.13 0.88 0.915 Osteophytes (all in mm 2 ) Femur lateral 7.6 (7.5) 3.32 5.26 2.72 to 3.93 10.31 0.716 Femur medial 7.1 (8.0) 5.44 6.84 4.66 to 6.23 13.41 0.579 Tibia lateral 10.0 (10.0) 2.49 4.77 1.94 to 3.03 9.35 0.867 Tibia medial 7.6 (5.9) 2.46 6.24 1.74 to 3.18 12.23 0.532 Other (mm, mm, degrees) Eminence lateral 12.5 (2.3) 0.59 1.13 0.46 to 0.72 2.21 0.864 Eminence medial 13.3 (1.8) 0.30 0.94 0.19 to 0.41 1.84 0.860 Joint angle -6.1 (3.4) -0.66 1.19 -0.80 to 0.52 2.33 0.924 95%CI Δ: 95% confidence interval of mean differences between the 2 observations; ICC: intraclass correlation coefficient; mean Δ: mean difference between the 2 observations of all radiographs; mm Al eq: mm aluminum equivalent; SD Δ: standard deviation of mean differences between the 2 observations; SDD: smallest detectable difference (1.96*SD of mean differences between the 2 observations).