Population-based study of the contribution of weather to hip fracture seasonality.

Previous studies have demonstrated seasonal increases in hip fracture incidence, but none have directly assessed the influence of inclement weather on this seasonality. In this study, the daily occurrence of hip fracture among women aged 45 years and older in Rochester, Minnesota, from 1952 through 1989 was ascertained using the resources of the Rochester Epidemiology Project and compared with the occurrence of inclement weather as recorded in hourly readings by the National Weather Service in Rochester for the same time period. Among the women aged 45-74 years, the risk of hip fracture was increased on days with snow (relative risk (RR) = 1.41, 95% confidence interval (CI) 1.10-1.81) or freezing rain (RR = 1.82, 95% CI 1.27-2.62). In this group, the elevated risk of hip fracture in winter, compared with summer (RR = 1.44, 95% CI 1.0-2.09), was reduced after controlling for weather (RR = 1.16, 95% CI 0.81-1.65). Among women aged 75 years and older, ice and snow were not strongly related to fracture occurrence. The winter-related increase in risk (RR = 1.16, 95% CI 0.96-1.40) was essentially unchanged after controlling for weather and was similar to the weather-adjusted seasonality of hip fracture occurrence in younger women. These data suggest that there are factors other than weather that may be linked to the seasonal pattern in hip fracture occurrence and that operate at all ages.