Mylène Jansen

222 Chapter 11 Table 2 : Intra-observer results for severe radiographs reanalyzed within 1 month Mean (SD) Mean Δ SD Δ 95%CI Δ SDD ICC Bone density (all in mm Al eq) Femur mean lateral 32.6 (4.4) 0.02 0.21 -0.02 to 0.06 0.41 0.999 Femur mean medial 36.8 (5.1) 0.02 0.23 -0.02 to 0.07 0.45 0.999 Tibia mean lateral 32.9 (5.2) -0.16 1.20 -0.40 to 0.08 2.35 0.973 Tibia mean medial 38.2 (5.2) 0.10 0.35 0.03 to 0.17 0.69 0.998 JSW (all in mm) Mean 5.3 (1.1) 0.07 0.39 -0.01 to 0.15 0.76 0.935 Mean lateral 7.7 (1.9) 0.17 0.73 0.03 to 0.32 1.43 0.923 Mean medial 2.9 (1.8) -0.03 0.24 -0.08 to 0.02 0.47 0.992 Minimum 1.0 (1.2) -0.04 0.31 -0.10 to 0.02 0.61 0.965 Osteophytes (all in mm 2 ) Femur lateral 8.6 (7.3) 0.80 2.73 0.25 to 1.34 5.35 0.928 Femur medial 11.1 (9.1) 2.04 5.69 0.90 to 3.18 11.15 0.806 Tibia lateral 11.8 (12.2) 0.77 5.90 -0.41 to 1.95 11.56 0.889 Tibia medial 8.5 (7.4) 0.01 5.58 -1.11 to 1.13 10.94 0.751 Other (mm, mm, degrees) Eminence lateral 12.7 (2.5) 0.17 1.14 -0.06 to 0.39 2.23 0.901 Eminence medial 13.3 (1.8) 0.06 0.89 -0.12 to 0.24 1.74 0.891 Joint angle -6.0 (3.6) -0.28 0.96 -0.47 to -0.08 1.88 0.962 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). Comparison of all 3 groups The mean of the parameters, the SD of the differences, the SDD and CV are shown for the 3 groups (all 293 radiographs with severe OA reanalyzed within a large period of time, the 98 radiographs with severe OA reanalyzed within 1 month, and 55 radiographs with mild OA from the original publication analyzed within 1 month) in Table 3. Besides increasing the ICC (comparing Tables 1 and 2), reanalyzing the severe OA radiographs within 1 month seemed to decrease the SDD and CV for almost all parameters. Furthermore, the SDD and CV for severe OA patients analyzed within 1 month were comparable to and often even better than those for mild OA patients for most parameters. Compared to mild OA, the SDD for severe OA was especially high for osteophyte parameters, although the CV, which corrects the SD for the mean overall values, was more comparable. For the tibia lateral bone density, the difference remained high in SDD and CV. Obviously, but importantly, all variables differed between mild and the severe OA in the expected direction, severe patients having a higher bone density, a smaller JSW, larger osteophytes, and higher eminetia.