Introduction: Osteoporosis is associated with increased risk for fracture. However, most postmenopausal women have bone mineral density (BMD) within the normal or osteopenic range. The aim of this study was to determine the proportion of the population burden of fragility fractures arising from women at modest risk for fracture.
Methods: We measured baseline BMD in a population-based random sample of 616 postmenopausal women aged 60-94 years and followed these individuals for a median of 5.6 years (IQR 3.9-6.5) to determine the incidence of fractures according to age, BMD and the presence of a prior fracture.
Results: Based on WHO criteria, 37.6% of the women had normal total hip BMD, 48.0% had osteopenia and 14.5% had osteoporosis. The incidence of fracture during follow-up was highest in women with osteoporosis, but only 26.9% of all fractures arose from this group; 73.1% occurred in women without osteoporosis (56.5% in women with osteopenia, 16.6% in women with normal BMD). Decreasing BMD, increasing age and prior fracture contributed independently to increased fracture risk; in a multivariate model, the relative risk for fracture increased 65% for each SD decrease in BMD (RR=1.65, 95%CI 1.32-2.05), increased 3% for every year of age (RR=1.03, 95%CI 1.01-1.06) and doubled with prevalent fracture (RR=2.01, 95% CI 1.40-2.88). A prevalent fracture increased the risk for fractures such that women with osteopenia and prevalent fracture had the same, if not greater, risk as women with osteoporosis alone.
Conclusions: Reducing the population burden of fractures requires attention to women with osteopenia, as well as osteoporosis, because over half of the fragility fractures in the population arise in these individuals, and women with osteopenia plus a prevalent fracture have the same fracture risk as women with osteoporosis.