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FRAX with or without BMD predicted fractures in obese, nonobese women
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WHO fracture risk algorithm scores with or without bone mineral density were useful models to predict clinical fractures in obese and nonobese women, according to data published in the Journal of Bone and Mineral Research.
The researchers used data from the Study of Osteoporotic Fractures (SOF) to compare the value of WHO fracture risk algorithm scores (FRAX) with and without BMD to predict fractures in postmenopausal women who were obese or not obese.
Of 6,049 women aged 65 years or older, data indicate 18.5% were obese and incident clinical fractures occurred in 26.9% of obese women by 2.2 years of follow-up, and 32.7% of nonobese women at 2.26 years of follow-up. Additionally, significantly lower femoral neck BMD was observed in nonobese women with fractures vs. obese women. Subsequently, 252 (22.5%) obese women compared with 1,215 (24.6%) nonobese women died by the 10-year follow-up.
Moreover, decision curve analysis showed that FRAX with or without BMD was useful to predict 10-year fracture probabilities in obese and nonobese women, according to researchers.
“For major osteoporotic fracture, the FRAX models were useful in women with predicted probabilities in the range of 10% to 30%, with very little difference between the net benefit of the two FRAX models in either obese or nonobese women,” the researchers wrote. “In the case of all clinical fractures, the FRAX models were not useful at threshold probabilities below around 30%, with only a small net benefit at probabilities in the range of 30% to 40%.”
Based on these findings, the researchers determined FRAX with and without BMD models are of similar worth in measuring hip and major osteoporotic fracture predictions in obese vs. nonobese women. Therefore, it is suggested that further randomized trials are completed to determine the efficacy of treatments among this patient population.
Disclosure: The researchers report no relevant financial disclosures.
Perspective
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Donald A. Bergman, MD
This study looked at whether the FRAX tool was reliable for calculating risk for fracture in obese women (defined as a BMI of 30 or greater). The data were obtained from the Study of Osteoporotic Fractures looking at women aged 65 and older. Although statistical analysis (using the receiver operator curve, a method of demonstrating how well prediction models discriminate) showed that using FRAX and BMD was better for predicting hip fracture in obese women, calibration data (agreement between predicted and observed risk) suggested that FRAX without including BMD in the calculation was a better predictor of overall risk for fracture. The article further points out that the negative predictive power of the National Osteoporosis Foundation (NOF) recommended thresholds for intervention are as good for obese as for non-obese women, meaning the obese women are no more likely to fracture than non-obese women who fall below the NOF recommended thresholds for treatment.
The biggest problem with using FRAX in predicting fracture risk for obese women is this: the FRAX score was designed to predict hip, wrist, humerus and spine fractures only. Obese women more typically get fractures of the leg, ankle and humerus. The statistical analysis presented seems to confirm that FRAX does not predict all fractures. Therefore, FRAX is useful in predicting some but not all fractures that are seen in obese women.
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