Gender Differences in Ankylosing Spondylitis Patients with Advanced Hip Involvement: Results from A Matched Retrospective Cohort Study

Objective To determine the gender differences in ankylosing spondylitis (AS) patients with advanced hip involvement. Methods We retrospectively analyzed the 373 consecutive AS patients with advanced hip involvement from 2012 to 2017 and divided them into two groups by sex with 340 men and 33 women. Research data on hip involvement in the patients were obtained from medical records and radiographs. The severity of radiographic hip involvement was evaluated by the Bath Ankylosing Spondylitis Radiology Hip Index (BASRI‐hip) scoring system. The data on clinical characteristics, radiographic hip involvement, and laboratory values were compared between the two groups. The comparison was performed again between the two groups after adjusting for the onset age and disease duration by propensity score matching (PSM). Results Men underwent total hip arthroplasty earlier than women in the patients, with a median age of 31 years (range, 19–67 years) vs 36 years (range, 23–67 years), respectively ( P  < 0.05). Hip involvement was found to be younger in men than that in women, with a median age of 18 years (range, 7–56 years) vs 23 years (range, 5–55 years) ( P  < 0.05), and men with bilateral onset in hips had a higher frequency than women with that (66.2% vs 39.4%) ( P  < 0.05). There was no gender difference in the proportion of bilateral advanced hip involvement (85.3% vs 72.7%) ( P  > 0.05). The proportion of the patients who had spinal involvement (89.1% vs 69.7%), flexion contracture in the hip (43.8% vs 24.2%), hip range of motion =0° (53.5% vs 30.3%), and an elevated level of C‐reactive protein (CRP) (69.1% vs 51.5%) was significantly higher in men than that in women ( P  < 0.05). After adjusting for the onset age and disease duration by PSM (1:1), men with bilateral onset in hips still had a higher frequency than women with that (76.7% vs 40.0%), and the proportion of the patients who had spinal involvement (90.0% vs 66.7%) and an elevated level of CRP (80.0% vs 53.3%) was significantly higher in men than that in women ( P  < 0.05). Conclusions The disease pattern of hip involvement in AS has gender differences, with bilateral onset being the dominant pattern in men and unilateral onset being more common in women. However, the frequency of bilateral advanced hip involvement has no gender difference eventually. The higher prevalence of spinal involvement in men with AS may be responsible for the more severe functional impairment compared with women.