Regional and gender-specific analyses give new perspectives for secular trend in hip fracture incidence.

In this study, we found that regional disparity in incidence of hip fractures has converged. Also, annual hip fracture risk ratios between genders have systematically diminished over time. INTRODUCTION Several studies have reported secular trends in hip fracture incidence, but knowledge about the possible causes is limited. We studied potential explanations by examining spatio-temporal epidemiology of the fractures and estimating relative risks between genders. METHODS This observational study was based on all inpatient hospital discharges in 1972-2018 in Finland. We divided the data by gender, 5-year age groups and Finnish sub-regions and estimated gender and age standardized spatio-temporal rates of hip fractures by using a Bayesian age-period-cohort model. RESULTS In 1972, women's hip fracture incidence was 1.2-1.3 times higher in western and coastal Finland compared to eastern and inland areas. Also, women had approximately 1.7 times higher average risk to get a hip fracture compared to men. Today, the hip fracture differences between the areas have converged to insignificant and the relative risk between genders has diminished to 1.2. Age-specific relative risks indicate greater hip fracture risk for younger men and older women, and the women's risk increases beyond the risk of men at age 65 which is ten years later than in the beginning of the study period. CONCLUSION Incidence of hip fracture has converged significantly between regions and genders. Especially factors related with socioeconomic development and increased frailty and longevity seem to be important. The hip fracture incidence rate ratio between women and men has systematically decreased in time, and more attention should be paid to hip fracture risk in men in the future.