Sex Differences in Outcomes of Total Hip Arthroplasty for the Treatment of Ankylosing Spondylitis
Ankylosing spondylitis (AS) is a chronic inflammatory disorder historically regarded as more prevalent in males, with earlier studies reporting a male-to-female ratio of approximately 3:1. However, recent epidemiological data suggest a trend toward gender homogeneity in disease prevalence. Despite this shift, female AS patients often experience prolonged diagnostic delays, leading to worse outcomes in disease activity, spinal mobility, functional capacity, and radiographic progression. Hip involvement, a common and debilitating manifestation of AS, affects approximately 25–33% of patients, profoundly impacting physical function, employment, and quality of life. Unlike the axial skeleton, where inflammation leads to new bone formation, hip pathology in AS primarily involves synovial inflammation, causing bone erosion and joint space narrowing. For patients with end-stage hip destruction, total hip arthroplasty (THA) remains a definitive treatment to restore mobility and alleviate pain. Although previous studies have explored THA outcomes in AS patients, the influence of gender on preoperative characteristics and postoperative results has not been systematically investigated. This study aimed to address this gap by comparing baseline demographics, clinical parameters, and surgical outcomes between male and female AS patients undergoing THA.
Study Design and Methodology
This retrospective cross-sectional analysis included 86 female AS patients (121 hips) who underwent THA between 2006 and 2019, alongside a control group of 468 male patients (663 hips). All participants met the modified New York criteria for AS diagnosis. The study received ethical approval, and informed consent was obtained from each patient. Data collection encompassed demographics, disease characteristics, preoperative clinical parameters, laboratory findings, and postoperative outcomes.
Patient Characteristics
Key demographic and disease-related variables were analyzed, including age at disease onset, age at surgery, disease duration, diagnostic delay, and presence of extra-articular manifestations (uveitis, inflammatory bowel disease [IBD], or psoriasis). Smoking history, preoperative hip range of motion (ROM), flexion contracture, and radiographic evidence of bony ankylosis were recorded. Laboratory markers such as erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), hemoglobin (HGB), and albumin (ALB) were assessed. Functional status and disease activity were quantified using the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) and Bath Ankylosing Spondylitis Functional Index (BASFI). Surgical outcomes were evaluated through clinician-reported outcomes (Harris Hip Score [HHS]) and patient-reported outcomes (12-Item Short Form Health Survey [SF-12] and satisfaction ratings).
Baseline Differences Between Genders
Statistically significant differences were observed in preoperative parameters between genders (Table 1). Female patients exhibited a later disease onset (median age: 23 vs. 21 years in males, P = 0.001) and underwent THA at an older age (median: 43 vs. 37 years, P = 0.002). Despite comparable disease duration (median: 18 vs. 15 years, P = 0.081) and diagnostic delay (7 vs. 6 years, P = 0.217), females showed distinct clinical profiles. Notably, uveitis was more prevalent in women (19.8% vs. 6.2%, P < 0.001), while males reported higher smoking rates (32.9% vs. 5.0%, P < 0.001). Preoperative hip flexion contracture was less severe in females (15° vs. 20°, P = 0.013), but no significant differences existed in total ROM or hip flexion.
Laboratory parameters revealed lower CRP levels in females (8.1 mg/L vs. 14.9 mg/L, P < 0.001) and reduced hemoglobin (120 g/L vs. 137 g/L, P < 0.001), aligning with known gender differences in systemic inflammation. Functional assessments indicated lower BASFI scores in females (46 vs. 56, P < 0.001), suggesting better baseline function despite comparable BASDAI scores (3.6 vs. 4.0, P = 0.141).
Surgical Outcomes and Follow-Up
Among females, 56 patients (82 hips) completed a median follow-up of 117.5 months (interquartile range [IQR]: 58–139 months), while 300 male patients (444 hips) had a median follow-up of 100.2 months (IQR: 60–133 months). Postoperative outcomes demonstrated significant improvements in both groups. In female patients, the median HHS increased from 39 (IQR: 27–46) preoperatively to 88 (IQR: 81–96) at final follow-up (P < 0.001). Similarly, SF-12 physical component summary (PCS) and mental component summary (MCS) scores improved from 36.6 to 46.2 and 43.0 to 51.4, respectively (P < 0.001 for both). BASDAI and BASFI scores also showed marked reductions (P < 0.001), reflecting diminished disease activity and enhanced functional capacity.
Comparative analysis between genders revealed no significant differences in postoperative outcomes. Final HHS (88 vs. 86, P = 0.374), SF-12 PCS (46.2 vs. 45.0, P = 0.420), and BASFI (22 vs. 24, P = 0.301) were comparable between females and males. Patient satisfaction rates mirrored these findings: 43 hips (52.4%) in females reported being “very satisfied,” versus 220 hips (49.5%) in males (P = 0.682).
Discussion
This study represents the largest comparative analysis of gender-specific outcomes following THA in AS patients. Despite baseline differences in age, inflammatory markers, and functional status, female patients achieved postoperative results equivalent to males. The absence of gender-based disparities in surgical outcomes challenges assumptions that delayed diagnosis or distinct disease phenotypes in females might compromise THA efficacy.
The higher prevalence of uveitis in females aligns with prior reports of sex-specific extra-articular manifestations. Conversely, elevated CRP and hemoglobin in males may reflect more pronounced systemic inflammation. The lower preoperative BASFI in females, despite similar disease duration, suggests potential gender differences in symptom reporting or pain tolerance. However, these distinctions did not translate into inferior surgical results, underscoring the robustness of THA in addressing end-stage hip pathology across genders.
While the study provides valuable insights, limitations include its retrospective design, potential variability in surgical techniques over the 13-year enrollment period, and incomplete long-term follow-up data. Furthermore, the focus on inpatients with severe hip involvement may have introduced selection bias, as these patients likely represent a subset with advanced disease, irrespective of gender.
Clinical Implications
These findings hold practical relevance for clinicians managing AS patients with hip involvement. The equivalence in THA outcomes between genders supports standardized surgical approaches and preoperative counseling. Female patients, despite later presentation and distinct clinical features, can anticipate functional improvements comparable to males. This underscores the importance of timely referral for THA in AS patients with progressive hip disease, regardless of gender.
Conclusion
Gender differences in AS extend to demographics, inflammatory profiles, and extra-articular manifestations. However, THA effectively mitigates hip-related disability in both sexes, with equivalent postoperative outcomes in pain relief, functional restoration, and patient satisfaction. These results reinforce THA as a reliable intervention for end-stage hip involvement in AS, irrespective of gender, and highlight the need for gender-neutral clinical guidelines in surgical management.
doi.org/10.1097/CM9.0000000000001782
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