Clinical characteristics and treatment patterns in ankylosing spondylitis patients undergoing total hip arthroplasty: a single-center retrospective cohort study with a two-decade comparative analysis (2001–2023)

Despite advances in medical treatment for ankylosing spondylitis (AS), total hip arthroplasty (THA) remains essential for managing advanced hip involvement. However, how the clinical characteristics and real-world treatment patterns of AS patients undergoing THA have evolved over the past two decades, and whether these trends differ according to age at disease onset, remains unclear. We conducted a retrospective cohort study of AS patients who underwent THA between 2001 and 2023. Patients were stratified by age at symptom onset (juvenile-onset AS [JAS]: ≤16 years; adult-onset AS [AAS]: >16 years) and surgery period (2001–2011 and 2012–2023). Demographics, clinical characteristics, laboratory parameters, and treatment patterns were compared between groups. Among 1,032 patients included, 204 (19.8%) were classified as JAS and 828 (80.2%) as AAS. Comparing 2001–2011 with 2012–2023, median age at surgery increased (36.0 vs. 42.0 years, P < 0.001), employment rate improved (69.3% vs. 82.5%, P < 0.001), and biologic agent use increased (0% vs. 10.5%, P < 0.001). JAS patients showed earlier disease onset (13.0 vs. 22.0 years, P < 0.001), shorter diagnostic delays (4.0 vs. 9.0 years, P < 0.001), but higher inflammatory markers (CRP: 20.9 vs. 11.9 mg/L, P < 0.001) compared to AAS patients. An increasing proportion of unilateral procedures was observed in both groups (JAS: 22.1% to 41.5%; AAS: 33.5% to 52.0%). This two-decade analysis described temporal changes in the clinical characteristics and management patterns of patients with ankylosing spondylitis (AS) undergoing total hip arthroplasty (THA), including increased use of biologic therapy. Within this THA-based surgical cohort, juvenile-onset AS (JAS) patients showed distinct clinical features compared with adult-onset AS (AAS) patients, including earlier disease onset and higher inflammatory burden. An increasing proportion of unilateral procedures was observed over time; however, the reasons for this trend cannot be determined from the present retrospective descriptive design and require further study.