Background Functional status and spinal mobility in patients with axial
spondyloarthritis (axSpA) are known to be determined both by disease activity
and by structural damage in the spine. The impact of structural damage in the
sacroiliac joints (SIJ) on physical function and spinal mobility in axSpA has
not been studied so far. The objective of the study was to analyze the impact
of radiographic sacroiliitis on functional status and spinal mobility in
patients with axSpA. Methods In total, 210 patients with axSpA were included
in the analysis. Radiographs of SIJ obtained at baseline and after 2 years of
follow up were scored by two trained readers according to the modified New
York criteria grading system (grade 0–4). The mean of two readers’ scores for
each joint and a sum score for both SIJ were calculated for each patient
giving a sacroiliitis sum score between 0 and 8. The Bath Ankylosing
Spondylitis Functional Index (BASFI) and Bath Ankylosing Spondylitis Metrology
Index (BASMI) at baseline and after 2 years were used as outcome measures.
Results Longitudinal mixed model analysis adjusted for structural damage in
the spine (modified Stoke Ankylosing Spondylitis Spine Score - mSASSS),
disease activity (Bath Ankylosing Spondylitis Disease Activity Index - BASDAI
and C-reactive protein level) and gender, revealed an independent association
of the sacroiliitis sum score with the BASFI: b = 0.10 (95% CI 0.01–0.19) and
the BASMI: b = 0.12 (95% CI 0.03–0.21), respectively, indicating that change
by one radiographic sacroiliitis grade in one joint is associated with
BASFI/BASMI worsening by 0.10/0.12 points, respectively, independently of
disease activity and structural damage in the spine. Conclusion Structural
damage in the SIJ might have an impact on functional status and spinal
mobility in axSpA independently of spinal structural damage and disease
activity. Trial registration ClinicalTrials.gov, NCT01277419. Registered on 14
January 2011
