Decreasing trend of inpatient mortality rates of aseptic versus septic revision total hip arthroplasty: an analysis of 681,034 cases

Background: While most revision total hip arthroplasties (rTHAs) are for aseptic loosening/instability, infection accounts for approximately 16%. The purpose of this study was to: (1) quantify mortality rates of aseptic versus septic rTHA; (2) determine if mortality rates have changed over the past 20 years; and (3) identify associated preoperative risk factors, focusing on the utility/validity of the Elixhauser comorbidity index (ECI). Methods: ICD-9/ICD-10 codes were used to identify patients undergoing rTHA in the National Inpatient Sample database between 1998 and 2017. A total of 681,034 cases (576,143 aseptic THA and 104,891 septic THA) were identified. For each patient, demographic variables including age, sex, race, insurance type, ECI, and inhospital mortality were gathered. A logistic regression model was constructed to assess risk of inhospital mortality. Results: From 1998 to 2017, inpatient mortality rates of aseptic and septic rTHA decreased from 0.83 to 0.45%, and from 2.58 to 1.24%, respectively. Septic rTHA was independently associated with higher odds of mortality relative to aseptic (odds ratio (OR): 2.305, 95% confidence interval (CI): (2.014, 2.638), p < 0.0001). Increased ECI was associated with higher odds of mortality at both medium (OR: 5.147, 95% CI: (4.433,5.977), p < 0.0001) and high index scores (OR: 13.714, 95% CI: (11.519,16.326), p < 0.0001). Conclusions: Mortality rates for both aseptic and septic rTHA have been declining over the past 20 years, potentially due to patient selection guidelines and advances in medical management. Our study confirms that the ECI is independently associated with increased inpatient mortality.