Geographical variations in hip fracture risk for women: strong effects hidden in standardised ratios

Abstract

There was 75% variation in the trend in hip fracture incidence with age in women aged 50 to 85 in France. In southwest France, the women are at higher risk of hip fracture at younger ages. This finding should be taken into account when examining risk factors. Few studies have analysed the geographical variations in the relationship between age and hip fracture incidence. Our goal was to assess these variations among women under 85 within the same country. The study population included women aged 50 to 85 who were living in France in 2004. Hip fracture cases were identified in the French Diagnosis Related Groups (DRG)-like database using the diagnosis code for closed hip fractures and procedural codes for treatment. The Moran index and a spatial model using latitude and longitude were used to assess the geographical heterogeneities of cumulative incidence risk (CIR) and age effect. A total of 29,218 hip fracture cases were identified. A south-to-north CIR gradient ranging from 7 to 16% was observed. The variation in the number of years until double hip fracture incidence was 75% (i.e. 1.49 to 2.57 years). In the south, and more markedly in southwest France, the women are at higher risk of hip fracture at a younger age. The risk of fracture may be different between women of the same age. This may be hidden in a comparison of standardised ratios. This finding should be considered when examining risk factors and implementing public health interventions.