MRI Characterization of Sacroiliac and Spinal Involvement in Spondyloarthritis: Prevalence, Distribution, and Associations with Inter-Rater Reliability

Abstract

Objective: To characterize the prevalence and distribution of sacroiliac (SI) joint and spinal magnetic resonance imaging (MRI) lesions in patients with spondyloarthritis (SpA), and to investigate associations with demographic characteristics, clinical factors (gender, smoking status, disease duration), and assess inter-rater reliability of MRI scoring.
Methods: Fifty-three SpA patients (75.5% male, mean age 34.0 ± 8.0 years) underwent MRI of the SI joints and spine. Lesion prevalence, regional distribution, and imaging severity scores were assessed. Associations with age, gender, smoking status, and disease duration were analyzed using appropriate statistical tests. Inter-rater reliability (IRR) for scoring was evaluated using Intraclass Correlation Coefficients (ICC) and Bland-Altman analysis.
Results: Fatty marrow infiltration was the most prevalent SI joint feature (96.2%), followed by sclerosis (73.6%) and erosions/joint space irregularities (69.8% each). Bone marrow edema (BME) was present in 67.9% of both SI joints and spine. Males demonstrated significantly greater spinal imaging scores than females (3.9 ± 4.1 vs 1.5 ± 2.3, p=0.049). Current smokers exhibited significantly higher spinal scores compared to non-smokers (5.4 ± 4.7 vs 2.5 ± 3.3, p=0.028). Longer disease duration was significantly associated with spinal fatty marrow replacement (p=0.003) and subchondral sclerosis (p=0.049). SI joint involvement showed no significant laterality or iliac vs. sacral predilection. Age correlated strongly with disease duration (r=0.607, p<0.001), and SI joint scores correlated moderately with spine scores (r=0.466, p<0.001). Inter-rater reliability was excellent for overall SI joint (ICC=0.956) and spine (ICC=0.970) scoring.
Conclusion: MRI effectively characterizes a spectrum of inflammatory and structural lesions in the SI joints and spine of SpA patients. Spinal disease severity appears greater in males and smokers. Specific spinal structural changes are associated with longer disease duration. The MRI scoring methods demonstrate high reliability, supporting their utility in clinical research.