Table 6

Multivariate stepwise linear regression analysis of clinical and imaging variables associated with the degree of radiographic progression in the spine as measured by the mSASSS in the FORCAST cohort of patients with SpA

Regression model	Adjusted R²	Significant variables	β coefficient	p Value
Primary model (age, sex, symptom duration, duration of follow-up, BL CRP, BL mSASSS, treatment)	0.054	Age	0.011	<0.001
		Duration of follow-up	0.004	0.03
		CRP	0.005	0.03
Primary model plus SSS fat metaplasia score	0.14	Age	0.011	0.002
		Duration of follow-up	0.010	0.002
		Fat metaplasia	0.027	<0.001
Primary model plus SSS erosion score	0.10	Age	0.015	<0.001
		CRP	0.006	0.02
		Duration of follow-up	0.011	0.002
Primary model plus SSS backfill score	0.10	Age	0.015	<0.001
		CRP	0.006	0.016
		Duration of follow-up	0.011	0.002
Primary model plus SSS ankylosis score	0.10	Age	0.015	<0.001
		CRP	0.006	0.018
		Duration of follow-up	0.011	0.002
Primary model plus SSS fat metaplasia, erosion, backfill, ankylosis scores	0.15	Age	0.010	0.01
		Duration of follow-up	0.011	0.001
		Fat metaplasia	0.025	0.001
		Ankylosis	0.012	0.047

BL CRP, Basile C-reactive protein; FORCAST, Follow Up Research Cohort in Ankylosing Spondylitis; mSASSS, modified Stoke Ankylosing Spondylitis Spine Score; SpA, spondyloarthritis; SPARCC, Spondyloarthritis Research Consortium of Canada; SSS, SPARCC MRI SIJ Structural Scoring.