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.