GEE results (OR; 95% CI; p values) for the outcome syndesmophyte formation according to reader 1 and reader 2, with MRI vertebral unit inflammation as determinant, and with adjustment for within-patient correlation by vertebral unit level and MRI reader (first line), for individual potential confounders (second to 11th line) and for all significant confounders (last line)*
| Adjustment factor | Active vertebral unit at baseline | Adjustment factor | Active vertebral unit at baseline only | Adjustment factor | Active vertebral unit at baseline and another time point | Adjustment factor | Active vertebral unit at any time point | Adjustment factor |
|---|---|---|---|---|---|---|---|---|
| Within-patient correlation | 1.85 (1.01 to 3.41) p=0.048 | NA | 2.06 (1.04 to 4.05) p=0.037 | NA | 1.11 (0.46 to 2.67) p=0.813 | NA | 1.77 (0.95 to 3.27) p=0.070 | NA |
| Gender | 1.75 (0.96 to 3.20) p=0.067 | 3.70 (1.01 to 13.48) p=0.048 | 1.93 (0.99 to 3.75) p=0.053 | NS | 1.14 (0.48 to 2.70) p=0.771 | 4.00 (1.18 to 13.61) p=0.026 | 1.67 (0.91 to 3.08) p=0.098 | NS |
| HLA-B27 | 1.91 (1.05 to 3.47) p=0.034 | 3.38 (1.14 to 9.99) p=0.028 | 2.11 (1.07 to 4.14) p=0.031 | 3.46 (1.16 to 10.27) p=0.026 | 1.16 (0.51 to 2.66) p=0.726 | 3.18 (1.08 to 9.42) p=0.036 | 1.85 (1.01 to 3.38) p=0.046 | 3.77 (1.27 to 11.18) p=0.017 |
| Age | 1.85 (0.98 to 3.52) p=0.060 | NS | 2.08 (1.02 to 4.23) p=0.044 | NS | 1.11 (0.43 to 2.90) p=0.829 | NS | 1.76 (0.92 to 3.34) p=0.086 | NS |
| Disease duration | 1.85 (0.99 to 3.43) p=0.052 | NS | 2.06 (1.04 to 4.10) p=0.040 | NS | 1.10 (0.45 to 2.68) p=0.836 | NS | 1.77 (0.95 to 3.28) p=0.073 | NS |
| BASDAI at baseline | 1.90 (0.96 to 3.76) p=0.065 | 0.63 (0.44 to 0.89) p=0.010 | 2.22 (1.06 to 4.64) p=0.034 | 0.63 (0.45 to 0.88) p=0.007 | 1.09 (0.40 to 2.95) p=0.866 | 0.64 (0.45 to 0.90) p=0.010 | 1.74 (0.88 to 3.45) p=0.114 | 0.60 (0.41 to 0.86) p=0.006 |
| BASDAI AUC | 1.91 (0.99 to 3.65) p=0.052 | NS | 2.20 (1.06 to 4.58) p=0.034 | 0.998 (0.997 to 1.000) p=0.046 | 1.07 (0.43 to 2.67) p=0.879 | NS | 1.76 (0.93 to 3.35) p=0.083 | NS |
| CRP at baseline | 1.73 (0.91 to 3.33) p=0.097 | NS | 1.82 (0.90 to 3.69) p=0.097 | NS | 1.27 (0.55 to 2.91) p=0.573 | NS | 1.62 (0.84 to 3.13) p=0.147 | NS |
| CRP AUC | 1.76 (0.95 to 3.27) p=0.072 | NS | 1.83 (0.93 to 3.58) p=0.079 | NS | 1.30 (0.63 to 2.70) p=0.475 | NS | 1.69 (0.91 to 3.13) p=0.097 | NS |
| Total mSASSS at baseline >5 | 1.72 (0.91 to 3.24) p=0.094 | NS | 1.95 (0.95 to 4.01) p=0.068 | NS | 1.02 (0.41 to 2.57) p=0.963 | NS | 1.66 (0.87 to 3.14) p=0.121 | NS |
| Syndesmophytes or bridging at baseline | 1.67 (0.88 to 3.18) p=0.116 | NS | 1.91 (0.92 to 3.96) p=0.084 | NS | 1.00 (0.38 to 2.63) p=0.995 | NS | 1.62 (0.84 to 3.10) p=0.147 | NS |
| Adjustment for all significant variables | 1.89 (0.98 to 3.65) p=0.056 | NA | 2.26 (1.08 to 4.74) p=0.031 | NA | 1.22 (0.47 to 3.15) p=0.678 | NA | 1.43 (0.59 to 3.49) p=0.426 | NA |
Statistically significant OR after adjustment for within-patient correlation (first line) and after adjustment for all significant confounders (last line) are highlighted in bold.
↵* All models adjusted for treatment effect (non-significant) and for within-patient correlation (by vertebral unit level and MRI reader).
AUC, area under the curve; BASDAI, Bath ankylosing spondylitis disease activity index; CRP, C-reactive protein; GEE, generalised estimating equation; HLA, human leucocyte antigen; mSASSS, modified Stoke AS spine score; NA, not applicable; NS, non-significant.