Incorporation of the anteroposterior lumbar radiographs in the modified Stoke Ankylosing Spondylitis Spine Score improves detection of radiographic spinal progression in axial spondyloarthritis

Table 4 Inter-observer reliability of the components of the mSASSS and the extended mSASSS

	Cervical spine lateral view	Lumbar spine lateral view	Lumbar spine AP view
ICC for the status score at baseline	0.91 (0.88, 0.93)	0.91 (0.88, 0.93)	0.86 (0.83, 0.90)
ICC for the status score at year 2	0.86 (0.82, 0.89)	0.92 (0.90, 0.94)	0.88 (0.84, 0.90)
ICC for the change score	0.49 (0.39, 0.59)	0.43 (0.32, 0.54)	0.30 (0.19, 0.44)
Kappa for the change score ≥ 2 points after 2 years	0.13 (− 0.04, 0.29)	0.38 (0.18, 0.57)	0.36 (0.18, 0.54)
Kappa for the development of new syndesmophytes after 2 years	0.38 (0.20, 0.55)	0.59 (0.42, 0.77)	0.40 (0.24, 0.57)
Kappa for the development of new/growth of existing syndesmophytes after 2 years	0.34 (0.17, 0.52)	0.62 (0.46, 0.79)	0.48 (0.32, 0.64)

Data are presented as intraclass correlation coefficient (ICC) and Cohen’s kappa coefficient to measure the inter-observer reliability for continuous and categorical variables, respectively, with a 95% CI
AP anteroposterior, mSASSS modified Stoke Ankylosing Spondylitis Spine Score, CI confidence interval, ICC intraclass correlation coefficient

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