Charlson Comorbidity Index and 28-day and 365-day mortality after ICU admission for hip fracture: a retrospective cohort study using MIMIC-IV

Background Mortality after hip fracture in intensive care unit (ICU) patients may reflect both acute critical illness and chronic disease burden. Whether the Charlson Comorbidity Index (CCI) retains prognostic information after adjustment for ICU severity remains unclear. We examined the association between CCI and 28-day and 365-day all-cause mortality in this high-acuity population. Methods We performed a retrospective cohort study using MIMIC-IV version 3.0. Adults with hip fracture, identified with ICD-9-CM code 820.x or ICD-10-CM codes S72.0-S72.2, were included if they were admitted to the ICU and had ascertainable survival status. CCI was analysed as the final processed score, both continuously and across integer-preserving categories: Q1 (0–4), Q2 (5–6), Q3 (= 7), and Q4 ( > = 8). Kaplan-Meier curves, Cox proportional hazards models, restricted cubic splines, sensitivity analyses, and exploratory concordance assessment were used. Results The cohort included 416 patients. Median age was 80.00 years (IQR, 65.75-88.00), 213 patients (51.2%) were women, and median CCI was 6.00 (IQR, 4.00-7.25). All-cause mortality was 15.14% at 28 days and 18.51% at 365 days. Mortality rose across CCI strata: 28-day mortality increased from 3.65% in Q1 to 30.77% in Q4, and 365-day mortality increased from 5.11% to 37.50%. In the fully adjusted model, each 1-point increase in CCI was associated with higher 28-day mortality (HR, 1.163; 95% CI, 1.039–1.302; P = 0.008) and 365-day mortality (HR, 1.168; 95% CI, 1.061–1.286; P = 0.002). Compared with Q1, Q4 showed the clearest excess risk for 28-day mortality (HR, 4.213; 95% CI, 1.474–12.046; P = 0.007) and 365-day mortality (HR, 5.131; 95% CI, 1.954–13.472; P < 0.001). Findings were stable in reduced sensitivity models. Restricted cubic splines showed an upward risk trajectory, with a statistically significant overall association for 365-day mortality. Conclusions In ICU patients with hip fracture, higher final processed CCI identified a clinically meaningful gradient in short-term and 1-year mortality. CCI may serve as a pragmatic marker of chronic host vulnerability that complements acute severity assessment.