The Interaction Effect Between Previous Stroke and Hip Fracture on Postoperative Mortality: A Nationwide Cohort Study

PURPOSE: It remains uncertain how a history of stroke impacts the prognosis for patients with hip fracture. This study aimed to evaluate mortality following hip fracture surgery by comparing patients with and without a history of stroke. PATIENTS AND METHODS: All patients aged 65 years or above in Denmark receiving hip fracture surgery between 2010 and 2018. For every patient, 10 individuals from the general population without hip fracture were sampled. Comparators had a similar stroke history, age, and sex on the date of hip fracture surgery (index date). We established four cohorts: hip fracture patients with/without stroke and non-hip fracture patients with/without stroke. Outcomes were all-cause mortality at 0–30 days, 31–365 days and 1 to 5 years. Direct standardized mortality rates (MR) with 95% confidence intervals (CI) were computed. We calculated the interaction contrast to estimate excess absolute mortality among patients with both hip fracture and stroke. Through a Cox proportional hazards model, we estimated the hazard ratio (HR) and the attributable proportion as a measure of excess relative mortality attributable to interaction. RESULTS: Of the hip fracture patients, 8433 had a stroke history and 44,997 did not. Of the non-hip fracture patients, 84,330 had a stroke history and 449,962 did not. Corresponding 30-day MRs/100 person years were 148.4 (95% CI: 138.8–158.7), 124.3 (95% CI: 120.7–128.1), 14.3 (95% CI: 13.4–15.2) and 8.4 (95% CI: 8.1–8.7). The interaction contrast was 18.2 (95% CI: 7.5–28.8), and the attributable proportion was 9.0% (95% CI: 2.9–15.1). No interaction was present beyond 30 days. CONCLUSION: We observed excess short-term mortality in patients with stroke and hip fracture, but the effect disappeared at later follow-up periods. Clinicians are encouraged to pay rigorous attention to early complications among hip fracture patients with stroke, as this may serve as a way to reduce mortality.