Days Alive and Out of Hospital at 15 Days after Hip Replacement May Be Associated with Long-Term Mortality: Observational Cohort Study

We aimed to evaluate the association between days alive and out of hospital (DAOH) and mortality at 15 days after a hip replacement. From March 2010 to June 2020, we identified 5369 consecutive adult patients undergoing hip replacements and estimated DAOH at 15, 30, 60, and 90 days after surgery. After excluding 13 patients who died within 15 days after surgery, receiver operating characteristic (ROC) curves were then generated to evaluate predictabilities for each follow-up period. We compared the mortality risk according to the estimated thresholds of DAOH at 15 days after hip replacement. ROC analysis revealed areas under the curve of 0.862, 0.877, 0.906, and 0.922 for DAOH at 15, 30, 60, and 90 days after surgery, respectively. The estimated threshold of DAOH during the 15 postoperative days was 6.5. Patients were divided according to this threshold, and propensity score matching was conducted. In a propensity score-matched population with 864 patients in each group, the risk of mortality increased in patients with a lower DAOH 15 (2.8% vs. 8.1%; hazard ratio [HR] = 3.96; 95% confidence interval [CI]: 2.24–6.99; p < 0.001 for one-year mortality, 5.2% vs. 13.0%; HR = 3.82; 95% CI: 2.33–6.28; p < 0.001 for three-year mortality, and 5.9% vs. 15.6%; HR = 3.07; 95% CI: 2.04–4.61; p < 0.001 for five-year mortality). In patients undergoing a hip replacement, DAOH at 15 days after surgery was shown to be associated with increased mortality. DAOH at 15 days may be used as a valid outcome measure for hip replacement.