Letters
Endocrinology
Volume 194 - Issue 12

Population and treatment-based incidence estimates of atypical fractures

Authors:  Christian M Girgis and Markus J Seibel

Med J Aust 2011; 194 (12): 666. || doi: 10.5694/j.1326-5377.2011.tb03163.x
Published online: 20 June 2011
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To the Editor: Atypical femur fractures appear to be an emerging adverse outcome of long-term use of bisphosphonates. Although analyses of epidemiological data suggest that subtrochanteric and diaphyseal fractures per se are rare,1,2 the true incidence of atypical fractures (a distinct subset of such fractures) is unknown.

In a recent 5-year retrospective study, we reviewed individual radiographs of 152 patients with subtrochanteric and diaphyseal femur fractures and identified 20 atypical fractures.3 Seventeen of these 20 atypical fractures had occurred in patients treated with oral bisphosphonates.

In light of these findings, we sought to calculate the incidence of atypical femur fractures in the population served by our large tertiary referral hospital in Sydney. According to the Australian Bureau of Statistics 2006 Census, the hospital’s catchment population (as defined by the New South Wales Department of Health) was 174 448. The annual incidence of atypical femur fractures in 2006 was therefore estimated to be 0.23 per 10 000 in the general population, and 1.6 per 10 000 in people aged over 65 years. These estimates, based on a stringent radiological definition of atypical femur fractures, confirm that, on a population basis, these fractures are indeed rare.

We also sought to define the mean annual incidence of atypical femur fractures in patients treated with oral bisphosphonates. Thus, we obtained data on the wholesale purchase of alendronate and risedronate by pharmacies within the hospital’s catchment area over the 5 years of the original retrospective study (1 June 2003 to 30 May 2008) from IMS Health Australia (market researchers for the global pharmaceutical and health care industries). A mean number of 2860 patients per year were prescribed alendronate and 1265 patients per year were prescribed risedronate. This corresponded to a mean annual incidence of atypical femur fractures of 10 per 10 000 in patients taking alendronate and three per 10 000 in those taking risedronate.

The use of a relatively small number of cases to calculate these incidences is a particular limitation of our research, and is a reflection of the rarity of these events. Furthermore, our estimates need to be considered within the wider context of the established beneficial effects of bisphosphonates in patients with osteoporosis. On the basis of randomised trials, it has been estimated that treating 1000 women with oral bisphosphonates for 3 years prevents 100 fractures.2 Also, several meta-analyses have confirmed significant reductions in the risk of osteoporotic vertebral and non-vertebral fractures in patients treated with oral bisphosphonates.4,5 In spite of two recent large database studies that showed a greater incidence of atypical fractures among long-term bisphosphonate users,6,7 atypical fractures are rare and the risks of using this class of drugs appears to be strongly outweighed by their proven efficacy in preventing fractures.

Authors

  • Christian M Girgis1
  • Markus J Seibel1
  • 1. University of Sydney, Sydney, NSW.

Correspondence: cgirgis@usyd.edu.au

Competing interests

Markus Seibel is a member of advisory boards for Merck Sharp and Dohme, Novartis, Amgen and Sanofi-Aventis. He has also received funding from these companies for institutional research.

References

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