Mylène Jansen

306 Chapter 15 with case-control matching, attempting to find a matched control patient for all treated (KJD and HTO) patients pre-treatment. Case-control matching was performed separately for the tibia (average of medial and lateral tibia) and femur (average of weight-bearing part of medial and lateral femur) and based on baseline T2 relaxation times as well as patient characteristics that had a significant influence on changes in T2 values in either group (treated or untreated). Tolerances were chosen as small as possible, while still ensuring the majority of treated patients could be matched with untreated OAI patients. Figure 1 : Example slice of the reconstructed T2 map within the lateral femoral and tibial region of interest, superimposed on a proton density weighted scan. Statistical analysis Baseline differences between the 3 groups (2 KJD groups because of the different indication) were calculated with 1-way ANOVA and, in case of statistically significant differences, post- hoc Tukey HSD tests. The intraclass correlation coefficient (ICC) between the 3 observers was calculated for all T2 relaxation times and cartilage volumes, for each of the regions separately and combining all time points, using a 2-way random model with absolute agreement. Assuming a good ICC for average measures, the results of the 3 observers were averaged to obtain the final T2 relaxation times and cartilage volumes. ICCs were interpreted according to the definitions of Koo and Li: an ICC <0.50 was considered poor, 0.50< ICC >0.75 was moderate, 0.75< ICC >0.90 was good, and ICC >0.90 was excellent. 29 Since previous research has shown that structural results are often significantly different between