Construction of a FRAX® model for the assessment of fracture probability in Canada and implications for treatment

Summary We describe the creation of a FRAX® model for the assessment of fracture probability in Canadian men and women, calibrated from national hip fracture and mortality data. This FRAX tool was used to examine possible thresholds for therapeutic intervention in Canada in two large complementary cohorts of women and men. Objective To evaluate a Canadian World Health Organization (WHO) fracture risk assessment (FRAX®) tool for computing 10-year probabilities of osteoporotic fracture. Methods Fracture probabilities were computed from national hip fracture data (2005) and death hazards (2004) for Canada. Probabilities took account of age, sex, clinical risk factors (CRFs), and femoral neck bone mineral density (BMD). Treatment implications were studied in two large cohorts of individuals age 50 years and older: the population-based Canadian Multicentre Osteoporosis Study (4,778 women and 1,919 men) and the clinically referredManitoba BMD Cohort (36,730 women and 2,873 men). Results Fracture probabilities increased with age, decreasing femoral neck T-score, and number of CRFs. Among women, 10.1–11.3% would be designated high risk based upon 10- year major osteoporotic fracture probability exceeding 20%. Amuch larger proportion would be designated high risk based upon 10-year hip fracture probability exceeding 3% (25.7– 28.0%) or osteoporotic BMD (27.1–30.9%), and relatively few from prior hip or clinical spine fracture (1.6–4.2%). One or more criteria for intervention were met by 29.2–34.0% of women excluding hip fracture probability (35.3–41.0% including hip fracture probability). Lower intervention rates were seen among CaMos (CanadianMulticentre Osteoporosis Study) men (6.8–12.9%), but in clinically referred men from the Manitoba BMD Cohort, one or more criteria for high risk were seen for 26.4% excluding hip fracture probability (42.4% including hip fracture probability). Conclusions The FRAX tool can be used to identify intervention thresholds in Canada. The FRAX model supports a shift from a dual X-ray absorptiometry (DXA)- based intervention strategy, towards a strategy based on fracture probability for a major osteoporotic fracture.