Test–retest data of spinal mobility instruments measured in RAPID-axSpA, 28-day interval
| N | Screening mean (SD) | Baseline mean (SD) | Mean difference (95% CI) | ICC (95% CI) | SDC | Data from literature | ||
| ICC | MCID/MCII/SDC | |||||||
| BASMI (0 to 10) | BASMI | |||||||
| axSpA | 218 | 3.6 (1.5) | 3.7 (1.6) | −0.12 (−0.20 to −0.05) | .93 (.91 to .95) | 0.6 | ICC rage 0.91–0.9737 39 41 | SDC range 0.82–0.9537 41 |
| r-axSpA | 117 | 4.2 (1.5) | 4.4 (1.5) | −0.19 (−0.31 to −0.08) | .91 (.87 to .94) | 0.6 | ||
| nr-axSpA | 101 | 3.0 (1.3) | 3.0 (1.4) | −0.05 (−0.15 to .06) | .93 (.90 to .95) | 0.5 | ||
| Modified Schober (cm) | Modified Schober | |||||||
| axSpA | 216 | 3.9 (2.2) | 3.8 (2.0) | .12 (−0.03 to .27) | .86 (.82 to .89) | 1.1 | ICC inter-observer range 0.75–0.9638 40 42 43; ICC intra-observer range 0.63–0.9438 40 43 | SDC 1.440 |
| r-axSpA | 116 | 3.5 (2.1) | 3.3 (2.0) | .15 (−0.05 to .36) | .85 (.79 to .90) | 1.1 | ||
| nr-axSpA | 100 | 4.4 (2.3) | 4.3 (1.8) | .09 (−0.14 to .31) | .85 (.78 to .90) | 1.1 | ||
| Lateral spinal flexion (cm) | Lateral spinal flexion | |||||||
| axSpA | 216 | 12.6 (6.6) | 12.1 (6.0) | .39 (−0.02 to .79) | .80 (.75 to .85) | 2.9 | ICC inter-observer range 0.–0.77-0.9838 40 42 43; ICC intra-observer range 0.65–0.9838 40 43 | SDC 5.140 |
| r-axSpA | 116 | 11.6 (7.3) | 10.3 (5.6) | .98 (.46 to 1.50) | .75 (.65 to .82) | 2.8 | ||
| nr-axSpA | 100 | 13.8 (5.6) | 14.1 (5.8) | −0.30 (−0.91 to .32) | .86 (.79 to .90) | 3.0 | ||
| Tragus-to-wall distance (cm) | Tragus-to-wall distance | |||||||
| axSpA | 218 | 13.5 (4.9) | 13.7 (5.0) | −0.19 (−0.46 to .07) | .92 (.90 to .94) | 1.9 | ICC inter-observer range 0.85–0.9838 42 43; ICC intra-observer range 0.94–0.9838 43 | |
| r-axSpA | 117 | 14.8 (5.8) | 14.9 (5.7) | −0.14 (−0.45 to .17) | .96 (.94 to .97) | 1.6 | ||
| nr-axSpA | 101 | 12.1 (3.0) | 12.4 (3.7) | −0.25 (CI −0.70 to .19) | .78 (.70 to .85) | 2.2 | ||
| Cervical rotation (degrees) | Cervical rotation | |||||||
| axSpA | 218 | 55.9 (20.9) | 54.7 (21.4) | 1.20 (−0.38 to 2.79) | .85 (.80 to .88) | 11.5 | ICC inter-observer range 0.69–0.9438 40 42; ICC intra-observer range 0.56–0.9538 40 | SDC 12.240 |
| r-axSpA | 117 | 48.5 (19.7) | 46.6 (19.7) | 1.89 (−0.62 to 4.41) | .76 (.67 to .83) | 13.4 | ||
| nr-axSpA | 101 | 64.4 (19.2) | 64.0 (19.3) | .40 (-1.40 to 2.21) | .89 (.84 to .92) | 8.9 | ||
| Intermalleolar distance (cm) | Intermalleolar distance | |||||||
| axSpA | 216 | 98.1 (25.8) | 96.6 (27.3) | 1.53 (−0.10 to 3.16) | .89 (.87 to .92) | 11.7 | ICC inter-observer 0.9342; ICC intra-observer 0.7240 | SDC 20.240 |
| r-axSpA | 116 | 94.5 (25.9) | 93.2 (28.2) | 1.40 (-1.06 to 3.85) | .88 (.83 to .92) | 12.9 | ||
| nr-axSpA | 100 | 102.2 (25.2) | 100.6 (25.7) | 1.69 (−0.39 to 3.76) | .92 (.88 to .94) | 10.2 | ||
| Chest expansion (cm) | Chest expansion | |||||||
| axSpA | 217 | 3.7 (2.2) | 3.7 (2.0) | −0.06 (−0.22 to .10) | .78 (.72 to .83) | 1.1 | ICC inter-observer range 0.55–0.85(40 42 43; ICC intra-observer range 0.63–0.9540 43 | SDC 2.240 |
| r-axSpA | 118 | 3.6 (2.5) | 3.4 (2.0) | .07 (−0.14 to .29) | .76 (.68 to .83) | 1.1 | ||
| nr-axSpA | 99 | 3.9 (1.8) | 4.2 (2.0) | −0.22 (−0.46 to .01) | .81 (.72 to .87) | 1.1 | ||
| Occiput-to-wall distance (cm) | Occiput-to-wall distance | |||||||
| axSpA | 218 | 3.7 (5.6) | 3.6 (5.5) | .06 (−0.19 to .30) | .95 (.93 to .96) | 1.8 | ICC inter-observer range 0.84–0.89(40 42 43; ICC intra-observer range 0.49–0.9440 43 | SDC 0.940 |
| r-axSpA | 118 | 4.5 (6.3) | 4.7 (6.4) | −0.11 (−0.41 to .19) | .97 (.96 to .98) | 1.6 | ||
| nr-axSpA | 100 | 2.6 (4.5) | 2.4 (3.7) | .25 (−0.14 to .65) | .88 (.83 to .92) | 1.9 | ||
BASMI, Bath Ankylosing Spondylitis Metrology Index (scores range from 0 to 10, higher scores signify greater impairment); ICC, intraclass correlation coefficient; MCID, minimal clinically important difference; MCII, minimal clinically important improvement; nr-axSpA, non-radiographic axSpA; RAPID-axSpA, a randomised placebo-controlled trial assessing efficacy and safety of certolizumab pegol for patients with radiographic and non-radiographic axSpA; r-axSpA, radiographic axSpA; SDC, smallest detectable change; SDD, SD of the mean difference of the two assessments
axSpA, axial spondyloarthritis; BASMI, Bath Ankylosing Spondylitis Metrology Index; ICC, intraclass correlation coefficient; MCID, minimal clinically important difference; MCII, minimal clinically important improvement; nr-axSpA, non-radiographic axSpA; r-axSpA, radiographic axSpA; SDC, smallest detectable change; SDC, smallest detectable change; SDD, SD of the mean difference.