Background Hip involvement in Ankylosing Spondylitis (AS) is the most frequent extraspinal manifestation and a common cause of disability and limited mobility, often ending with hip replacement. There are few studies analysing the radiographic changes of the hip and their relationship with other disease variables.

Objectives To determine the factors associated with radiographic hip involvement and its prevalence.

Methods A cross-sectional study was performed based on patients with AS, excluding the patients with associated psoriasis or inflammatory bowel disease. To assess radiographic hip involvement, we scored the last anteroposterior pelvic radiograph performed using the Bath Ankylosing Spondylitis Radiology Index (BASRI). Demographic, clinical, laboratory and radiographic data were collected and analysed. We considered the presence of hip disease with a BASRI-hip grade of at least 2. Statistical analysis: A descriptive study was performed. To compare differences we used a 1-way ANOVA test and Pearson chi-square. The statistical analyses were done using SPSS 24.0. p≤0.05 was considered statistically significant.

Results 215 patients were identified, with a mean age of 52±13.6 years and 76.7% of the patients were male. The age at onset was 25.29±8.22 years. 86.4% of the patients were HLA-B27-positive. Regarding their treatment, 27.9% were under biological therapy. A hip replacement was needed in 14 patients (0.7%), with 6 of them requiring a bilateral hip replacement. The mean BASDAI score, BASFI score and ASDAS CRP index were 4.01±6.31; 4.73±8.8 and 2.17±1.01 respectively.

The table shows the comparison between the two groups based on the presence of hip involvement (BASRI hip ≥2). Statistically significant differences were observed in the age, age at onset and presence of peripheral arthritis. Patients with hip involvement had higher scores in BASFI score, ASDAS CRP and ESR. Axial radiographic involvement assessed with axial BASRI score and total SASSSm was associated with hip disease and a significant association was seen between hip involvement and metrological parameters.

Conclusions Radiographic hip involvement assessed with BASRI score is prevalent and it is related with the age at onset, disease activity and the presence of peripheral arthritis. These patients present more disability, less mobility and greater axial radiographic involvement.

Disclosure of Interest None declared