Thirty-Day Mortality After Hip Fracture Surgery: Association with In-Hospital Adverse Events and Comparative Performance of Comorbidity Indices

Background/Objectives: Hip fractures are associated with high short-term mortality in older adults. This study aimed to determine 30-day mortality after hip fracture surgery and evaluate factors associated with short-term mortality, with particular attention to baseline comorbidity indices and in-hospital adverse events. Methods: This retrospective cohort study included 785 patients who underwent surgery for hip fracture at University Hospital of Split, Croatia, between January 2021 and December 2022. Clinical data were extracted from medical records. The primary outcome was 30-day mortality, including in-hospital and post-discharge deaths. Associations with mortality were examined using univariable and multivariable logistic regression. Baseline-only comorbidity models were constructed using the American Society of Anesthesiologists Physical Status Classification System (ASA PS Classification), the Charlson Comorbidity Index (CCI), and the Elixhauser Comorbidity Index (ECI). Exploratory hospital-course models additionally included in-hospital adverse events, which were interpreted as time-dependent hospital-course events rather than baseline predictors. Results: 30-day mortality was 11.0% (86/785). Older age, male sex, higher comorbidity burden, and in-hospital adverse events were associated with mortality. Mortality was 5.7% without documented adverse events, 24.2% with one adverse event, and 42.4% with two or more adverse events. Baseline-only comorbidity models showed acceptable and broadly comparable discrimination, with AUCs of 0.73–0.77. Exploratory hospital-course models showed higher discrimination, with AUCs of 0.80–0.82. Conclusions: 30-day mortality after hip fracture surgery was associated with baseline patient vulnerability and in-hospital adverse events. Baseline-only models based on the ASA PS Classification, the CCI, and the ECI provided broadly comparable short-term risk stratification. In-hospital adverse events should be viewed as markers of an adverse clinical trajectory, not evidence of causality.