Contribution of clinical risk factors to bone density-based absolute fracture risk assessment in postmenopausal women

Hip fractures are independently associated with advancing age, specific clinical risk factors (CRFs), and low bone mineral density (BMD). The use of BMD T-scores for quantifying fracture risk ignores the contribution of age and CRFs. We previously developed a mathematical model of absolute hip fracture risk that incorporates patient age, BMD, and the results of eleven specific CRFs. The purpose of this study was to compare the contribution of an approach to fracture risk stratification using the full model (age, CRFs and BMD) with that of a unidimensional BMD-only model. We selected 213 consecutive postmenopausal females (mean age 65.3, range 50-87.9) with CRF data referred for BMD assessment of fracture risk. Absolute hip fracture risk (over the next 5 years and remaining lifetime) was estimated using both the full and BMD-only models. The mean ratio of absolute hip fracture risks (BMD-only/full model) derived for each patient was 0.8 (95% CI, 0.16-4.0) for hip fracture in the next 5 years and 1.1 (CI, 0.1-7.6) for remaining lifetime. The wide confidence intervals indicate a large contribution of age and CRFs to fracture risk stratification. Categorization of women as 'high risk' was frequently discordant for the two models. One-half of the women designated 'high risk' under the full model were classified as 'low risk' based upon BMD alone. In conclusion, we have shown that a multidimensional approach to hip fracture risk stratification is feasible, and greatly modifies risk stratification based on BMD alone.