Table 1.
Characteristics of the study population, both overall and stratified by the presence or absence of cervical facet joint ankylosis during any period of follow-up
| No. with data | Total patients (n = 1106) |
≥ 1 cervical facet joint ankylosis | |||
|---|---|---|---|---|---|
| Presence (n = 230) | Absence (n = 876) | P-value | |||
| Baseline parameters | |||||
| Age, mean ± SD years | 1106 | 31.4 ± 9.4 | 34.8 ± 8.2 | 30.5 ± 9.5 | < 0.001 |
| Male sex, n (%) | 1106 | 976 (88.2%) | 220 (95.7%) | 756 (86.3%) | < 0.001 |
| Symptom duration, years | 892 | 7.0 (3.0–13.0) | 11.5 (6.0–17.0) | 6.0 (2.0–12.0) | < 0.001 |
| HLA-B27 positivity, n (%) | 1101 | 1062 (96.5%) | 225 (97.8%) | 837 (96.1%) | 0.288 |
| ESR, mm/h | 865 | 22.0 (7.0–46.0) | 40.0 (19.0–60.0) | 18.0 (5.0–41.5) | < 0.001 |
| CRP, mg/dL | 705 | 1.2 (0.8–2.7) | 1.9 (1.3–3.3) | 1.0 (0.8–2.3) | < 0.001 |
| BASDAI (0–10), mean ± SD | 263 | 5.1 ± 2.7 | 5.5 ± 2.6 | 5.0 ± 2.7 | 0.162 |
| Sacroiliitis grade (0–4)a, mean ± SD | 1052 | 2.8 ± 0.9 | 3.5 ± 0.6 | 2.6 ± 0.9 | < 0.001 |
| Hip involvementb, n (%) | 1084 | 110 (10.1%) | 41 (18.6%) | 26 (3.1%) | < 0.001 |
| Cervical facet joint score (0–15) | 1106 | 0.0 (0.0–0.0) | 6.0 (2.0–13.0) | 0.0 (0.0–0.0) | < 0.001 |
| Cervical mSASSS (0–36) | 1106 | 6.0 (4.0–8.7) | 14.4 (7.6–28.0) | 5.5 (3.9–7.1) | < 0.001 |
| Total mSASSS (0–72) | 1106 | 7.5 (5.0–15.8) | 27.0 (11.8–51.8) | 6.7 (5.0–10.0) | < 0.001 |
| ≥ 1 bridging syndesmophyte at baseline, n (%) | 1106 | 167 (15.1%) | 110 (47.8%) | 11 (1.3%) | < 0.001 |
| Longitudinal parameters | |||||
| Duration of follow-up, mean ± SD years | 1106 | 8.3 ± 2.8 | 9.0 ± 2.9 | 8.1 ± 2.8 | < 0.001 |
| No. of spinal radiographs, mean ± SD | 1106 | 4.5 ± 1.2 | 4.8 ± 1.3 | 4.4 ± 1.2 | < 0.001 |
| Smoking ever, n (%) | 1052 | 639 (60.7%) | 159 (72.3%) | 480 (57.7%) | < 0.001 |
| Uveitis ever, n (%) | 930 | 352 (37.8%) | 98 (47.1%) | 254 (35.2%) | 0.002 |
| Peripheral arthritis ever, n (%) | 920 | 391 (42.5%) | 68 (33.0%) | 323 (45.2%) | 0.002 |
| Use of TNF inhibitors ever, n (%) | 1106 | 580 (52.4%) | 153 (66.5%) | 427 (48.7%) | < 0.001 |
| ≥ 1 bridging syndesmophyte during any period of follow-up, n (%) | 1106 | 299 (27.0%) | 186 (80.9%) | 34 (3.9%) | < 0.001 |
Values are presented as median (interquartile range) for continuous variables unless indicated otherwise and n (%) for categorical variables
aCalculated by averaging the grades of the right and left sacroiliac joints according to the modified New York criteria
bDefined as a BASRI-hip score of at least grade 2
BASDAI, Bath Ankylosing Spondylitis Disease Activity Index; BASRI-hip, Bath Ankylosing Spondylitis Radiology Hip Index; CRP, C-reactive protein; ESR, erythrocyte sedimentation rate; HLA, human leucocyte antigen; mSASSS, modified Stoke Ankylosing Spondylitis Spine Score; SD, standard deviation; TNF, tumour necrosis factor