Elective primary total hip arthroplasty in rheumatoid arthritis versus osteoarthritis: in-hospital outcomes from the national inpatient sample, 2016–2021

Abstract Background Whether coded rheumatoid arthritis (RA) among patients undergoing elective total hip arthroplasty (THA) is associated with excess short-term inpatient morbidity in contemporary U.S. practice remains uncertain. Methods We performed a retrospective cohort study using the National Inpatient Sample (2016–2021). Adults undergoing elective primary THA were identified using ICD-10-CM/PCS codes. The exposure cohort included admissions with coded RA in any diagnosis position. The comparator cohort included admissions with narrow primary hip osteoarthritis (OA) as the principal diagnosis and no RA. Propensity scores were estimated from demographic, socioeconomic, hospital, and comorbidity variables. Inverse probability of treatment weighting (IPTW) with survey weighting was used for the primary analysis, followed by doubly adjusted regression models that included age and all variables with persistent post-weighting imbalance greater than 0.10 (female sex, osteoporosis, chronic obstructive pulmonary disease, chronic anemia, depression, and race). Additional sensitivity analyses included stricter weight truncation, a restriction analysis, conventional multivariable modeling, and sex-stratified analyses addressing residual sex imbalance. Results A total of 274,582 admissions met eligibility criteria; 274,539 were included in the final analytic cohort after exclusion of 43 records with missing or invalid propensity-weight inputs. The analytic cohort included 7,264 RA admissions and 267,275 OA admissions. In the primary weighted analysis, RA was associated with higher odds of acute blood loss anemia (OR 1.30, 95% CI 1.23–1.38), red blood cell transfusion (OR 1.40, 95% CI 1.23–1.60), acute kidney injury (OR 1.47, 95% CI 1.26–1.71), non-home discharge (OR 1.27, 95% CI 1.19–1.36), and a composite hematologic/renal in-hospital complication (OR 1.31, 95% CI 1.24–1.39).RA was also associated with slightly longer length of stay (+ 0.14 days, 95% CI + 0.10 to + 0.19) and modestly higher total hospital charges (+$1,018, 95% CI +$89 to +$1,947). Findings were directionally consistent across sensitivity analyses, including stricter weight truncation, restriction to admissions with principal OA plus concomitant RA, and sex-stratified analyses. Conclusions In this contemporary national THA cohort, coded RA was associated with a small but consistent increase in in-hospital complication and resource-utilization burden compared with OA. These findings should be interpreted as adjusted associations rather than causal effects, and the modest effect sizes should not be overstated. They may provide context for perioperative risk assessment and discharge planning among patients with coded RA undergoing elective THA.