The World Health Organization Fracture Risk Assessment Tool (FRAX) underestimates incident and recurrent fractures in consecutive patients with fragility fractures.

Context: The World Health Organization Fracture Risk Assessment tool (FRAX) was developed to identify patients at risk of sustaining a fragility fracture (FF).

Objective: The objective of the study was to evaluate estimated FRAX probabilities of FF at the time of a FF and to compare them with the observed incidence of recurrent FF.

Methods: A prospective cohort included men and women older than 50 years at the time of a FF. FRAX scores without bone mineral density [FRAX-body mass index (BMI)] were calculated prior to and after the inclusion FF. Recurrent FFs were recorded over a 4-year follow-up. Determinants associated with recurrent FF were determined by univariate and multivariate analyses.

Results: FRAX-BMI scores were available in 1399 of the 1409 recruited patients. A high-risk FRAX-BMI score was present in only 42.7% patients before and 56.4% after the incident FF. Most FF patients at low or moderate risk before their initial FF were men, younger than 65 years, or without previous FF. Over a median follow-up of 3 years, recurrent FF occurred in 108 patients (2.69 per 100 patient-years). The overall sensitivity of post-FF FRAX to predict a recurrent FF was 71.3% and was specifically lower in patients younger than 65 years (13%) and without previous FF (63%) at inclusion.

Conclusions: The FRAX-BMI scores were below the Canadian threshold for treatment in more than half the patients at the time of a FF and in close to a third of patients with recurrent FF. FRAX-BMI severely underestimates the FF risk in patients younger than 65 years old and after a single FF.