Geographic and seasonal variations in hip fracture incidence in Sweden: a nationwide population-based study.

RATIONALE: To investigate geographic and seasonal differences in the occurrence of hip fracture within Sweden in the years 2020-2022. MAIN RESULTS: There were differences in hip fracture incidence rates depending on geographic location as well as sex and season. SIGNIFICANCE: Unexplained differences in hip fracture occurrence remain, warranting further investigation. PURPOSE: To investigate geographic differences in hip fracture incidence in Sweden and to explore potential factors underlying this variation. METHODS: The populations of people ≥ 60 years of each Swedish county were identified using the Total Population Register. First hip fractures occurring between 2020 and 2022 were identified in the National Patient Register. Sex-, and County specific as well as seasonal hip fracture incidence rates were calculated. Stratified Poisson regression was used to compare incidence in the first quarter of the year with that in the remaining quarters. Additionally, sex stratified adjusted Poisson regression was performed to compare the incidence in Stockholm with other counties. RESULTS: 2,879,444 individuals were included in the study. Hip fracture incidence rates varied across Swedish counties, with the age standardized rate per 10,000 person-years ranging from 54 (Kalmar) to 67 (Västernorrland) in women and from 35 (Södermanland) to 52 (Norrbotten) in men. Incidence tended to be lower during the summer months, except among women 60-79 years in southern Sweden. Seasonal variations were most pronounced among men 60-79 years in northern Sweden. Geographic differences persisted after adjusting for age, income level, care dependency, hospital frailty risk score, place of birth, and usage of fall-risk increasing drugs. CONCLUSION: Geographic disparities in first hip fracture incidence were observed among both women and men in Sweden, with the highest rates in the northernmost counties. These differences could not be fully explained by uneven distribution of the risk factors examined in this study. Additionally, sex differences were noted in the counties with the highest and lowest incidence rates. Seasonal variation in hip fracture incidence was evident.