Fracture Risk Assessment

Scientific research now supports the use of proven therapies to prevent osteoporotic fractures based on the individual's probability of fracture as opposed to their bone density score alone.

This new concept has been validated to ensure its accuracy and reproducibility by a WHO working group (established in 1998) in collaboration with IOF and the (US) National Osteoporosis Foundation. The  easy-to-use fracture risk assessment tool for family physicians to use with patients of both sexes, all ages, ethnic groups and in all countries is called the FRAX^TM - WHO Fracture Risk Assessment Tool.

Below is an overview of the concept behind the WHO approach to fracture risk assessment .

Background and overview

For many years bone mineral density measurements have provided the standard method of assessing the risk of fracture, based on the WHO classification of osteoporosis as a bone mineral density 2.5 standard deviations or more below the BMD of a young individual (T-score²-2.5). However, this approach captures only a small proportion of those individuals who will suffer a fracture and hence if treatment is targeted only at such individuals, the global impact of intervention will not be as efficient.

Hip fracture risk is five times higher at age 80 than at age 50, although both individuals may have the same BMD values

Assessment of fracture risk can be improved by the use of clinical risk factors which act independently of bone mineral density to increase the risk of fracture, and this forms the basis of the WHO approach. The aims are to optimize sensitivity (i.e. detection rate) of fracture risk prediction using a case finding strategy in men and women that can be widely implemented in primary care.

To achieve this, the predictive value of clinical risk factors has been studied in a number of large, prospectively studied population-based cohorts with a broad geographical representation. In total, 59,232 men and women have been studied to provide information over nearly 250,000 ‘person years’.

Easily identifiable risk factors shown to improve the prediction of fracture risk include the following:

Individually the presence of these risk factors were shown to increase the risk of hip fracture at least 1.5 to 2-fold after adjustment for bone mineral density.

Awareness of which risk factors are manageable within a bone healthy lifestyle is important, such as smoking cigarettes and alcohol use, versus those that are out of one's control. Many studies indicate that low intake of calcium is a risk factor for hip fracture, and while quantifying calcium intake in general practice is difficult, all osteoporosis guidelines include recommendations for both calcium and vitamin D intake or supplementation. And of course high-impact exercise is a positive contributor to bone mineral density.

Some of these risk factors vary in importance according to age. For example, risk factors for falling - such as visual impairment, reduced mobility and treatment with sedatives - are more strongly predictive of fracture in the elderly than in younger individuals.

Glucocorticoid use is an important cause of osteoporosis and fractures. Bone loss is believed to be most rapid in the first few months of treatment, with the most significant loss at the spine (vertebra). However, the risk of hip fracture in this population is higher in younger ages.

A history of fragility fracture is an important risk factor for future fracture - in fact the risk is approximately doubled. This risk is even more marked for a vertebral fracture following a previous spine fracture, up to a 12-fold increase at any given BMD. As discussed, this risk increases with age.

In the WHO model, fracture risk is expressed as an absolute risk in terms of 10-year fracture probability (the % likelihood that an individual will sustain a fracture in the next 10 years), rather than as a T-score. This accommodates life expectancy and is more easily understood by both health professionals and patients. According to nation-specific healthcare priorities, wealth and health expenditure, intervention thresholds can then be set that are based on the cost-effectiveness of treatment at given fracture probabilities.

In conclusion, this approach provides a practical tool with which fracture risk may be assessed in individual patients in clinical practice. In some individuals, for example those with a history of previous fragility fractures, or elderly individuals on high doses of glucocorticoids, fracture probability based on these risk factors alone will be sufficiently high to exceed the cost-effective intervention threshold, and bone mineral density measurements will not be required. In others, the absence of any risk factors will indicate a risk that is sufficiently low to exclude the need for bone mineral density assessment. In the remainder of individuals, bone mineral density measurements may be used in combination with clinical risk factors to determine whether fracture probability attains or exceeds the intervention threshold.

The model thus improves the prediction of fracture risk in clinical practice, enabling more accurate targeting of treatment and resulting in greater cost-effectiveness in the prevention of osteoporotic fractures.

 

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