Polymyositis has minimal effect on primary total knee or hip arthroplasty outcomes.

To assess whether polymyositis is associated with more complications and higher healthcare utilization after total knee or hip arthroplasty (TKA/THA). Using the 1998-2014 U.S. National Inpatient Sample data, we performed multivariable-adjusted logistic regression analyses to assess the association of polymyositis with in-hospital complications (implant infection, revision, transfusion, mortality) and healthcare utilization (hospital charges, length of hospital stay, discharge to non-home setting), controlling for important covariates and confounders. Sensitivity analyses additionally adjusted the main models for hospital location/teaching status, bed size, and region. Of the 4,116,485 THAs and 8,127,282 TKAs, 853 people with polymyositis had THAs (0.02%) and 1038 had TKAs (0.01%). In multivariable-adjusted analyses, compared to people without polymyositis, people with polymyositis had similar odds of hospital charges above the median, hospital stay > 3 days, and discharge to non-home setting post-TKA and post-THA. Polymyositis was associated with significantly lower odds ratio (OR; 95% confidence interval [CI]) of revision and mortality post-THA, 0.44 (0.36, 0.55) and 0.63 (0.48, 0.84), but not post-TKA, 2.98 (0.47, 18.95) and 4.40 (0.61, 31.64), respectively. Findings from the main analyses were confirmed in the sensitivity analyses. People with polymyositis had no increase in healthcare utilization post-TKA/THA. A lower revision rate and mortality post-THA in people with polymyositis need further confirmation. Study findings should reassure the key stakeholders about the benefits of TKA/THA, including people with polymyositis.