Ankylosing spondylitis substantially increases health-care costs and length of hospital stay following total hip arthroplasty – National in-patient database study

Introduction: The outcome following major arthroplasty surgeries in patients with ankylosing spondylitis (AS) has tremendously improved over the past decades, due to substantial amelioration in the medical therapies and sophistication of available surgical modalities. Although various studies have already demonstrated the complication rates and challenges faced in AS patients undergoing THA, there is a substantial paucity of data on the actual healthcare burden associated with this disease, and the diverse factors which may affect it. Methods: Using the National Inpatient Sample (NIS) database (on the basis of ICD-10 CMP codes), patients undergoing THA between the years 2016 and 2019 were identified. These patients were then classified into two categories: group A: patients with a known diagnosis of AS; and group N: those without. The details regarding demographical information, associated co-morbidities, data pertaining to patients’ hospital admissions including expenditure incurred, length of stay and complications encountered, were compared. In addition, propensity-score matching was performed to identify a 1:1 matched sample of THA patients without AS. Results: Overall, 367,890 patients underwent THA; among whom, 501 (0.14%) were known AS patients (group A). Group A included a substantially higher proportion of patients belonging to younger age group (58.6 ± 13.4 versus 65.9 ± 11.4 years; p < 0.001), male sex (67.1% in group A vs 44.1% in group N; p < 0.001), and Asian ethnicity (p < 0.001). Group A patients had a substantially higher risk for longer duration of hospital stay (p < 0.03) and higher overall healthcare expenditure incurred (p < 0.001). As compared to group N, AS patients had a significantly higher risk for developing post-operative anemia [21.8% (group A) vs 11.8% (group N); p < 0.02]; and higher rate of periprosthetic infections [2.4% (group A) vs 1.0% (group N); p < 0.007]. Conclusion: Patients with AS require a significantly longer duration of hospital stay and higher admission-related expenditure following THA, as compared to the general population. These enhanced early health care-associated costs can be attributed to higher complication rates in AS patients. AS patients are prone to higher rates of anemia and peri-prosthetic infections during the early post-THA period.