Table 4:

Frequency of 5 MRI lesion types based on affected sacroiliac joint quadrants

SIJ quadrants affected	BME	Erosion	Fat metaplasia	Backfill	Ankylosis
Mean ± SD	0.86 ±1.45	0.05 ±0.15	0.98 ±3.55	0.04±0.23	1.02 ±3.45
Median (IQR)	0 (0–1.3)	0 (0–0)	0 (0–0)	0 (0–0)	0 (0–0)
n (%) with ≥ 1 quadrants	10 (30)	1 (3)	2 (6)	1 (3)	2 (6)
n (%) with ≥ 2 quadrants	7 (21)	0 (0)	1 (3)	0 (0)	2 (6)
n (%) with ≥ 3 quadrants	5 (15)	0 (0)	1 (3)	0 (0)	2 (6)
n (%) with ≥ 4 quadrants	2 (6)	0 (0)	1 (3)	0 (0)	2 (6)
n (%) with ≥ 5 quadrants	2 (6)	0 (0)	1 (3)	0 (0)	2 (6)
n (%) with ≥ 6 quadrants	1 (3)	0 (0)	1 (3)	0 (0)	2 (6)
n (%) with ≥ 7 quadrants	0 (0)	0 (0)	1 (3)	0 (0)	2 (6)

Mean (SD) and median (IQR) of SIJ quadrants: pooled over 3 readers. n (%) with ≥1 to ≥7 SIJ quadrants: number of subjects (percentage) having ≥1 to ≥7 SIJ quadrants affected by a given lesion type as concordantly reported by ≥2/3 readers.

BME=Bone marrow edema