Table 2

Reliability (κappa values) for detection of active and structural MRI lesions in the SIJ by seven readers from the ASAS MRI group who assessed MRI scans from the ASAS Classification cohort

Mean κ of all reader pairs (95% CI)Median κ of all reader pairsRange of κ for all reader pairs
All available MRI scans (n=278)
(Data for structural lesions available from 238 scans)
ASAS-positive MRI0.75 (0.66 to 0.83)0.750.64–0.86
Subchondral bone marrow oedema0.65 (0.56 to 0.74)0.650.53–0.75
Inflammation at the site of erosion0.30 (0.13 to 0.47)0.300.15–0.53
 Capsulitis0.40 (0.14 to 0.66)0.420.19–0.72
 Joint fluid0.36 (0.21 to 0.50)0.360.18–0.53
 Enthesitis0.21 (0.05 to 0.37)0.170.03–0.56
 Sclerosis0.43 (0.30 to 0.55)0.420.20–0.62
 Erosion0.55 (0.44 to 0.66)0.530.40–0.69
 Fat lesion0.59 (0.47 to 0.71)0.580.41–0.72
Fat metaplasia in an erosion cavity0.46 (0.27 to 0.66)0.470.22–0.65
 Bone bud0.13 (−0.05 to 0.30)0.12−0.04–0.56
 Ankylosis0.53 (0.21 to 0.83)0.490.28–0.91
MRI scans with consecutive DICOM images
(Data for active and structural lesions available from 160 and 148 scans, respectively)
ASAS-positive MRI0.73 (0.61 to 0.84)0.730.60–0.86
Subchondral bone marrow oedema0.60 (0.49 to 0.72)0.600.47–0.69
Inflammation at site of erosion0.37 (0.15 to 0.58)0.370.18–0.73
 Capsulitis0.55 (0.18 to 0.90)0.560.29–0.80
 Joint fluid0.41 (0.23 to 0.59)0.410.27–0.57
 Enthesitis0.23 (0.03 to 0.45)0.20−0.04–0.66
 Sclerosis0.48 (0.33 to 0.63)0.520.25–0.68
 Erosion0.61 (0.47 to 0.75)0.640.41–0.74
 Fat lesion0.61 (0.46 to 0.76)0.610.32–0.78
Fat metaplasia in an erosion cavity0.50 (0.26 to 0.74)0.470.25–0.71
 Bone bud0.11 (−0.06 to 0.29)0.06−0.06–0.60
 Ankylosis0.58 (0.25 to 0.89)0.590.32–0.91
  • ASAS, Assessment of SpondyloArthritis international society; DICOM, digital imaging and communications in medicine ; SIJ, sacroiliac joint.