Radiographic Hip Involvement in Ankylosing Spondylitis: Factors Associated with Severe Hip Diseases

Objective. To determine the factors associated with severe radiographic hip involvement in patients with ankylosing spondylitis (AS). Methods. A cross-sectional retrospective study was performed. The patients were classified into 3 groups based on the Bath Ankylosing Spondylitis Radiology Hip Index (BASRI-hip): minimal hip disease, moderate hip disease, and severe hip disease. Demographic, clinical, radiographic, and laboratory data were collected and analyzed. To identify factors associated with severe hip disease, ordinal regression analyses were performed. Results. A total of 256 patients were involved in the study. There were differences in the age at onset, delay in diagnosis, bilateral hip involvement, sacroiliitis, Schober's index, and occiput-to-wall distance among the 3 groups (p < 0.05). The patients with severe hip disease had lower C-reactive protein and erythrocyte sedimentation rate levels than did the minimal group (p < 0.05). The functional status based on the Bath Ankylosing Spondylitis Functional Index and the Harris Hip Score showed significant differences (p < 0.05). The results of the ordinal regression analyses showed that bilateral hip involvement, sacroiliitis, delay in diagnosis, age at onset, and spinal involvement were associated with a higher BASRI-hip (p < 0.05). Conclusion. Bilateral hip involvement, severe sacroiliitis, longer delay in diagnosis, early disease onset, and spinal involvement are associated with severe hip disease in patients with AS. The severity of hip involvement is associated with the functional status in AS.