Table 5.

Impact of pretreatment Ankylosing Spondylitis Disease Activity Score (ASDAS) on spinal radiographic progression introduced to address the issue of confounding by indication

Variable	OR	95% CI	P value
Prior TNFi up to the start of X-ray interval yes/no	0.15	0.04 to 0.56	0.01
Baseline sacroiliac damage (0–7) at start of each X-ray interval	1.26	0.92 to 1.72	0.16
Female sex	0.31	0.06 to 1.52	0.15
Symptom duration	1.05	1.00 to 1.11	0.05
Current smoking	2.29	0.56 to 9.40	0.25
HLA-B27 negative	1.07	0.17 to 6.66	0.95
NSAID use at start of each X-ray interval	0.71	0.18 to 2.83	0.63
ASDAS at start of TNFi and ASDAS at inclusion for non-treated patients	1.06	0.62 to 1.81	0.82

Analysis in 226 patients and 352 X-ray intervals (16 events).

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