East-west gradient in hip fracture incidence in Spain: how much can we explain by following the pattern of risk factors?

Our objective was to analyze the incidence and trend of hip fracture in Spain and its distribution by Autonomous Community (AC). In Spain, the age-adjusted incidence rate of hip fracture is decreasing. There is great variability in the incidence and tendency of hip fracture among the different ACs. Genetic, demographic, and climatic factors and cohort effect factors of the civil war explain 96% of this variability. INTRODUCTION: In Spain, there is great variability between the different Autonomous Communities (ACs) in the incidence of hip fracture. The objectives of our study are (1) to estimate the incidence rate and trend of hospital admissions for hip fracture in Spain and by ACs and (2) to analyze risk factors/markers that could explain the variability in the incidence and trend between different ACs. METHOD: This work includes 2 studies (TREND-HIP and VAR-HIP). TREND-HIP: retrospective, national, observational study based on the administrative database of the National Health System that includes a Minimum Basic Data Set (MBDS) of hospital admissions. VAR-HIP: ecological study based on the analysis of the results obtained in TREND-HIP study, with different risk factors/markers obtained from different sources. RESULTS: In the 17 years included in the analysis, there were 744,848 patients diagnosed with hip fracture. The global age-adjusted rate of hip fracture at the national level was 315.38/100,000 person*year (95% CI 312.36-317.45); by AC, the rate varied from 213.97 in the Canary Islands to 363.13 in the Valencia and Cataluña communities. We observe an east-west gradient in Spain. The trend for both sexes was - 0.67% (95% CI 0.9990-0.9957) (p < 0.001). In the analysis of risk factors/markers that explain this distribution, we found significant correlations with genetic factors, demographics, climatic factors and the time a region was on the Republican side of the civil war. The linear regression model that includes the factors that show significant correlation explains 96% of the variability observed. CONCLUSION: In Spain, the age-adjusted incidence rate for hip fracture is decreasing. There is a great variability in the incidence and tendency of hip fracture among the different ACs. Genetic, demographic, climatic factors and the cohort effect of the civil war explain 96% of this variability.