A position paper from the International Osteoporosis Foundation (IOF) and the International Society for Clinical Densitometry (ISCD), published in Osteoporosis International, has reported that many of the limitations of the FRAX (fracture risk assessment tool) algorithm will have to remain for the time being.
Introduced in 2008, FRAX is an algorithm that allows primary care physicians to use clinical risk factors, such as prior fragility fracture, to calculate a patient’s risk of fracture. Although widely used, FRAX does have several limitations.
According to Kanis et al, the authors of the position paper, the simplicity of FRAX is seen as a benefit in primary care but is also seen as a limitation. “The risk of fracture increases with exposure to glucocorticoids, but FRAX only accommodates a yes/no response to the relevant questions.”
FRAX also only allows a “yes/no” for the presence of prior fractures despite the fact that both the number and severity of vertebral fractures could help to calculate the risk of a future fracture.
“The evidence is less clear that the number of prior fractures at other sites is a determinant of fracture risk, though there is good evidence that past vertebral, humeral and hip fractures are more predictive of future fractures than are fractures at other sites.”
The problem with amending FRAX to include the length of exposure to gluccorticoids, the number of prior fractures, and the exposure of other relevant clinical risk factors is that it would require “the collection of new population cohorts”, which would need to include information on the risk of fracture associated with these exposures and their interaction with other variables in the FRAX algorithm. However, regarding the number of fractures, Kanis et al advise: “In the absence of quantitative information, the clinician should recognise that fracture probabilities should be upward revised in patients with a history of multiple prior fractures (ie, more than average) and greater weight accorded to prior vertebral, hip, or humeral fracture than to fractures at other sites.”
Another, widely criticised, limitation of FRAX is that it does not include the presence of falls or the risk of falls. Falls are strongly associated with fractures, and an IOF/ISCD clinical task force “strongly recommended” that they should be incorporated into FRAX. The problem again is how this is to be achieved as there are several reasons why including falls into FRAX is difficult: existing data on falls is not of “adequate quality” to add to FRAX; the risk of falls are “inherently” taken into account in the algorithm; and the data on whether intervention for falls decreases the risk of fracture is insufficient (as the aim of FRAX is to identify factors that are amenable to treatment). Kanis et al report: “The only sound advice is that individuals who fall more frequently than average are likely to have a higher fracture probability than that provided by FRAX”. They add that patients who fall less frequently than average are likely to have a lower risk of fractures than that observed by FRAX.
In their conclusion, Kanis et al state that FRAX is “far from perfect, but it is better than BMD [bone mineral density] alone….the wish list of clinicians for the modulation of FRAX is large and in many instances, these wishes cannot be presently fulfilled.” They add that although most of the limitations have to remain for the time being, understanding these limitations may be helpful to using FRAX in clinical practice.
John Kanis, professor emeritus at Sheffield University, said that the paper was based on an international meeting devoted to FRAX. “The major benefit of the meeting was to increase the understanding of FRAX to the academic community so that its application to primary care can be facilitated.”