| Summary: | The risk of a recurrent fragility fracture is high following a first fracture and higher still with more than one prior fracture. This study provides adjustments to FRAX-based fracture probabilities accounting for the number of prior fractures. Introduction: Prior fractures increase subsequent fracture risk. The aim of this study was to quantify the effect of the number of prior fractures on the 10-year probability of fracture determined with FRAX®. Methods: The study used data from the Reykjavik Study fracture register that documented prospectively all fractures at all skeletal sites in a large sample of the population of Iceland. Ten-year probabilities of hip fracture and major osteoporotic fracture (MOF) were determined according to the number of prior osteoporotic fractures over a 20-year interval from the hazards of death and fracture. Fracture probabilities were also computed for a prior osteoporotic fracture irrespective of the number of previous fractures. The probability ratios provided adjustments to conventional FRAX estimates of fracture probability according to the number of prior fractures. Results: Probability ratios to adjust 10-year FRAX probabilities of a hip fracture and MOF increased with the number of prior fractures but decreased with age in both men and women. Probability ratios were similar in men and women and for hip fracture and MOF. Mean probability ratios according to the number of prior fractures for all scenarios were 0.95, 1.08, 1.21 and 1.35, for 1,2, 3 and 4 or more prior fractures, respectively. Thus, a simple rule of thumb is to downward adjust FRAX-based fracture probabilities by 5% in the presence of a single prior fracture and to uplift probabilities by 10, 20 and 30% with a history of 2, 3 and 4 or more prior fractures, respectively. Conclusion: The probability ratios provide adjustments to conventional FRAX estimates of fracture probability according to the number of prior fractures.
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