Table 2

GEE results (OR; 95% CI; p values) for the outcome syndesmophyte formation according to reader 1 or 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 two lines)*

Adjustment factorActive vertebral unit at baselineAdjustment factorActive vertebral unit at baseline onlyAdjustment factorActive vertebral unit at baseline and another time pointAdjustment factorActive vertebral unit at any time pointAdjustment factor
Within-patient correlation1.64 (1.12 to 2.41) p=0.012NA1.50 (0.95 to 2.35) p=0.079NA1.69 (0.90 to 3.17) p=0.105NA1.72 (1.20 to 2.44) p=0.003NA
Gender1.57 (1.08 to 2.28) p=0.0182.79 (1.45 to 5.40) p=0.0021.44 (0.94 to 2.22) p=0.0982.81 (1.45 to 5.44) p=0.0021.66 (0.89 to 3.09) p=0.1092.89 (1.48 to 5.67) p=0.0021.64 (1.16 to 2.33) p=0.0052.73 (1.41 to 5.28) p=0.003
HLA-B271.64 (1.12 to 2.41) p=0.011NS1.50 (0.95 to 2.36) p=0.079NS1.69 (0.90 to 3.17) p=0.103NS1.72 (1.21 to 2.46) p=0.003NS
Age1.65 (1.12 to 2.43) p=0.011NS1.50 (0.95 to 2.37) p=0.083NS1.70 (0.90 to 3.20) p=0.101NS1.73 (1.21 to 2.46) p=0.003NS
Disease duration1.64 (1.11 to 2.40) p=0.012NS1.49 (0.95 to 2.35) p=0.083NS1.68 (0.90 to 3.15) p=0.106NS1.71 (1.20 to 2.44) p=0.003NS
BASDAI at baseline1.67 (1.13 to 2.47) p=0.010NS1.56 (0.98 to 2.46) p=0.059NS1.66 (0.89 to 3.09) p=0.111NS1.74 (1.21 to 2.49) p=0.003NS
BASDAI AUC1.68 (1.14 to 2.48) p=0.0090.999 (0.998 to 1.000) p=0.0461.56 (0.98 to 2.47) p=0.0610.999 (0.998 to 1.000) p=0.0491.67 (0.89 to 3.13) p=0.109NS1.73 (1.21 to 2.47) p=0.0030.999 (0.998 to 1.000) p=0.021
CRP at baseline1.58 (1.06 to 2.34) p=0.024NS1.41 (0.89 to 2.25) p=0.145NS1.73 (0.91 to 3.30) p=0.096NS1.65 (1.15 to 2.38) p=0.007NS
CRP AUC1.57 (1.06 to 2.32) p=0.025NS1.41 (0.89 to 2.25) p=0.144NS1.70 (0.90 to 3.23) p=0.105NS1.64 (1.14 to 2.35) p=0.008NS
Total mSASSS at baseline >51.55 (1.06 to 2.25) p=0.0232.59 (1.29 to 5.20) p=0.0071.43 (0.92 to 2.22) p=0.1152.63 (1.31 to 5.29) p=0.0071.60 (0.86 to 2.97) p=0.1362.63 (1.30 to 5.29) p=0.0071.63 (1.15 to 2.31) p=0.0062.40 (1.20 to 4.80) p=0.014
Syndesmophytes or bridging at baseline1.57 (1.07 to 2.30) p=0.0212.58 (1.36 to 4.87) p=0.0041.44 (0.92 to 2.24) p=0.1092.64 (1.40 to 4.98) p=0.0031.64 (0.87 to 3.08) p=0.1242.67 (1.41 to 5.05) p=0.0031.62 (1.14 to 2.32) p=0.0082.39 (1.27 to 4.50) p=0.007
Adjustment for all significant variables1.51(1.05 to 2.19) p=0.028NA1.43 (0.92 to 2.20) p=0.109NA1.57 (0.85 to 2.89) p=0.150NA1.55 (1.01 to 2.19) p=0.012NA
Adjustment for all significant variables1.56 (1.07 to 2.27) p=0.020NA1.46 (0.95 to 2.26) p=0.088NA1.62 (0.87 to 3.02) p=0.130NA1.57 (1.10 to 2.24) p=0.012NA
  • Statistically significant OR after adjustment for within-patient correlation (first line) and after adjustment for all significant confounders (last two 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).

  • Adjusted for ‘total mSASSS at baseline >5’.

  • Adjusted for presence of ‘syndesmophytes or bridging at baseline’ (at the patient level, according to both readers).

  • 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.