Table 1 Demographics and baseline disease characteristics

Age, y

31.7 (7.9)

31.7 (7.5)

0.94^c

31.9 (6.7)

Male, n/N (%)

105/163 (64.4)

45/76 (59.2)

0.44^d

12/22 (54.5)

Symptom duration, years

2.4 (1.8)

1.5 (0.9)

< 0.001^c

1.5 (0.9)

Current smoker, n/N (%)

37/163 (22.7)

29/75 (38.7)

0.01^d

5/22 (22.7)

HLA-B27(+), n/N (%)

121/157 (77.1)

66/76 (86.8)

0.08^d

17/22 (77.3)

BASDAI (0–10)

6.0 (1.8)

3.4 (2.0)

< 0.001^c

4.5 (2.1)

ASDAS

3.0 (1.0)

2.1 (0.9)

< 0.001^c

2.6 (0.9)

BASFI (0–10 cm VAS)

4.1 (2.4)

2.0 (1.9)

< 0.001^c

3.1 (2.9)

CRP, mg/L

7.4 (11.5)

6.0 (8.1)

0.19^c

7.1 (13.0)

Erosion SSS (0–40)^f

2.2 (3.0)

2.8 (3.5)

0.12^c

0.6 (1.5), 2.4 (4.7), 1.5 (2.6)

Backfill SSS (0–20)

0.5 (1.3)

0.3 (0.7)

0.50^c

NA

Fat metaplasia SSS (0–40)^f

0.6 (1.7)

0.5 (1.8)

0.91^c

1.5 (3.2), 1.8 (3.7), 1.7 (3.9)

Ankylosis SSS (0–20)^f

0.3 (1.3)

0.2 (1.1)

0.11^c

0.1 (0.6), 0.1 (0.3), 0.2 (0.7)

SPARCC MRI SIJ inflammation score (0–72)^f

8.5 (11.0)

6.0 (9.4)

0.003^c

4.5 (6.5), 3.3 (4.0), 2.7 (3.9)

SPARCC MRI SIJ inflammation score ≥ 2, n/N (%)^f

99/161 (61.5)

33/76 (43.4)

0.009^d

11/20 (55.0), 9/19 (47.4), 9/21 (42.9)

Total SIJ score (mNY grade 0–8)^f

1.5 (1.3)

1.6 (1.6)

0.76^c

1.5 (2.2), 1.4 (2.0), 1.7 (1.6)

SIJ radiograph met mNY criteria (%)^{e, f}

19/156 (12.2)

10/68 (14.7)

0.61^d

7/22 (31.8), 5/20 (25.0), 4/21 (19.0)