Mylène Jansen

KIDA performance in severe OA 219 11 depend on the mean absolute values which may influence the comparison of these absolute values between mild and severe OA patients, the coefficient of variation (CV), a measure expressing variability relatively to the average value of the measurements, was calculated as well, by dividing the SD of the differences between observations by the mean value of both observations and multiplying that by 100 (%). To compare KIDA parameters with the most frequently used grading system for OA, individual KIDA parameters were compared to the overall KL grade. This was done using separate linear regression models, using only 1 (the most recent) analysis result for each of the radiographs analyzed with a larger time period (years). As an additional explorative analysis, the influence of the mean of the measurements (of the 2 observations) and of the KL grade (both separately, as measure for severity) on the absolute intra-observer difference between 2 measurements was analyzed for all parameters. For this, linear regression was used on the data of severe OA patients re-analyzed within 1 month (to ensure that results will not be biased by a long period of time between analyses); a p- value <0.05 was considered statistically significant. Results Patients In total, 293 radiographs with double KIDA readings were available, taken at baseline (n=103), 1-year follow-up (n=98), and 2-year follow-up (n=92). The radiographs were taken of 103 different patients, of whom 61 were treated with KJD and 42 with HTO. The mean KL grade of the patients was 2.7. The median time difference between the first and second analysis was 50 months (interquartile range 39 – 52 months). Of the 100 radiographs that were reanalyzed within 1 month, it was discovered that for 2 radiographs the process of randomization was not correct and, as a result, they were not included for analysis twice. As such, these were excluded, and double analysis results within 1 month were available for a total of 98 radiographs. These were images of patients treated with KJD (n=56) and HTO (n=42) and taken at baseline (n=37), 1 year (n=29) and 2 years (n=32). The average KL grade was 2.6. Results for all severe radiographs reanalyzed within a large period of time The Bland-Altman plots for 3 relevant example parameters evaluated in all 293 radiographs are shown in Figure 2. Plots for all other parameters of these patients can be found in Supplementary Figures S1 – 5.