Assessment of the Prevalence and Characteristics of Hip Involvement in Spondyloarthritis: Results From a Rheumatology Outpatient Center

AIM: Hip involvement is a well-recognized feature of axial spondyloarthritis (AS). This study aimed to assess the prevalence of hip involvement and its relationship with both symptomatic and structural severity in a cohort of AS patients treated in an outpatient rheumatology clinic. METHODS: This retrospective, single-center study was conducted from 2019 to 2023 and included confirmed AS patients. Hip involvement was defined as hip pain related to AS-driven inflammation, confirmed by radiographic imaging (Bath Ankylosing Spondylitis Radiology Hip Index, or BASRI, score of ≥2). Demographic data and parameters of both symptomatic and structural severity were collected. The risk of hip involvement based on disease duration was evaluated using Kaplan-Meier analysis. RESULTS: Among 137 AS patients, 89 were men (65.0%), and 48 (35.0%) were women. The mean age was 42.2 years (SD ±14, range: 18-76), and the mean disease duration was 7.5 years (SD ±9.1, range: 0.5-38). Radiographic evidence of hip involvement was present in 19 patients (13.9%): unilateral in 9 patients (6.6%) and bilateral in 10 patients (7.3%). Hip involvement was more common in men, those with longer disease duration, and those with a higher incidence of uveitis. Patients with hip involvement exhibited higher symptomatic (Bath Ankylosing Spondylitis Disease Activity Index, or BASDAI, and Ankylosing Spondylitis Disease Activity Score, or ASDAS) and structural (modified Stoke Ankylosing Spondylitis Spine Score, or mSASSS) severity scores. In terms of disease duration, 18.6% of male patients had hip involvement after 10 years, rising to 48.8% after 20 years. CONCLUSION: Hip involvement is a frequent manifestation of AS, often presenting bilaterally and associated with longer disease duration and greater disease severity. However, its prevalence appears lower in outpatient settings compared to university hospital series.