Table 8.

Sensitivity analysis: integrating a third reading of radiographs for the multivariable analysis for identification of factors associated with radiographic SIJ progression defined as a change of at least one grade in at least one SIJ and ignoring a change from 0 to 1

Variable	A.TNFi use before the 2-year radiographic interval			B.TNFi use during the 2-year radiographic interval
	OR	95% CI	P value	OR	95% CI	P value
Prior TNFi use up to the start of X-ray interval yes/no	0.50	0.28 to 0.89	0.02
TNFi use during X-ray interval≥1 year				0.46	0.27 to 0.78	<0.01
TNFi use during X-ray interval<1 year				0.57	0.18 to 1.84	0.35
Baseline sacroiliac damage at start of each X-ray interval (0–7)	1.12	0.97 to 1.29	0.12	1.11	0.97 to 1.28	0.13
Female sex	0.74	0.44 to 1.26	0.27	0.73	0.43 to 1.26	0.26
Symptom duration	1.00	0.97 to 1.03	0.99	1.00	0.97 to 1.03	0.93
Current smoking	1.29	0.76 to 2.18	0.35	1.23	0.73 to 2.08	0.43
HLA-B27 negative	1.99	1.04 to 3.80	0.04	1.91	1.00 to 3.66	0.05
NSAID use at start of each X-ray interval	0.72	0.40 to 1.29	0.27	0.71	0.40 to 1.28	0.26
ASDAS at start of each X-ray interval	0.85	0.64 to 1.14	0.28	0.95	0.72 to 1.25	0.69

Three hundred one patients with 477 intervals (87 events).

ASDAS, Ankylosing Spondylitis Disease Activity Score; BASDAI, Bath Ankylosing Spondylitis Disease Activity Index; CRP, C-reactive protein; HLA-B27, human leucocyte antigen B27; NSAID, non-steroidal anti-inflammatory drug; SIJ, sacroiliac joint; TNFi, tumour necrosis factor inhibitor.