Background/Purpose: To analyze the association between the presence of structural damage in the sacroiliac joints and physical function / spinal mobility in patients with axial spondyloarthritis (SpA), which has not been investigated so far.

Methods: A total of 210 patients with early axial SpA (105 patients with radiographic axial SpA and symptom duration up to 10 years and 95 patients with non-radiographic axial SpA and symptom duration up to 5 years) from the German Spondyloarthritis Inception Cohort (GESPIC) were included in this cross-sectional analysis. Pelvic radiographs were scored by two trained readers (DP, HH) in a concealed and randomly selected order according to the grading system of the modified New York criteria (grade 0 to 4). For the current analysis, a mean of two readers score was calculated for each sacroiliac joint. A sum of two sacroiliitis grades (left and right sacroiliac joints) was calculated for each patient giving a total sacroiliitis score between 0 and 8. Structural damage in the spine was assessed by the same readers according to the modified Stoke Ankylosing Spondylitis Spine Score (mSASSS). Disease activity was assessed by the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) and C-reactive protein (CRP), functional status by the Bath Ankylosing Spondylitis Functional Index (BASFI), and spinal mobility – by the Bath Ankylosing Spondylitis Metrology Index (BASMI).

Results: In the univariable linear regression models, the crude parameter estimates for the association between sacroiliitis score and BASFI / BASMI were 0.09 (95%CI -0.07 to 0.25) and 0.23 (95%CI 0.11 to 0.33), respectively. After adjustment for parameters, which could be associated with radiographic sacroiliitis and might have an impact on the outcome (function / spinal mobility) – structural damage in the spine (mSASSS), disease activity (BASDAI and CRP), and gender – the parameter estimates indicating an association between sacroiliitis score and BASFI / BASMI changed to 0.10 (95%CI -0.01 to 0.21) and 0.12 (95%CI 0.01 to 0.23), respectively. These data indicates that change by one radiographic sacroiliitis grade in one joint is associated with a BASFI / BASMI worsening by 0.10 / 0.12 points irrespectively of structural damage in the spine and disease activity.

Conclusion: Presence of structural damage in the sacroiliac joints has an impact on functional status spinal mobility independently of structural damage in the spine and disease activity in patients with axial SpA, an association which had been mostly neglected previously.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/functional-relevance-of-structural-damage-in-the-sacroiliac-joints-in-patients-with-axial-spondyloarthritis-results-from-the-german-spondyloarthritis-inception-cohort/