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A recent population-based study suggested that long-term bisphosphonate use raised risk for atypical femoral fractures involving the subtrochanteric region or shaft (JW Gen Med Mar 3 2011). Now, investigators have reviewed fractures that occurred during 2008 among all older Swedish women (age, ≥55). Of 1271 subtrochanteric or femoral shaft fractures, 59 were atypical according to strict radiological criteria.
The relative risk for atypical fracture associated with bisphosphonate use, compared with no use, was 47.3; this corresponded to 5 additional cases per 10,000 patient-years of bisphosphonate use. In a comparison between the 59 atypical cases and 263 controls with typical subtrochanteric or shaft fractures, 78% of cases and 10% of controls had used bisphosphonates (adjusted odds ratio, 33.3). This elevated risk was similar with use of alendronate and risedronate, and was not further increased with concomitant use of corticosteroids or proton-pump inhibitors. Likelihood of atypical fracture rose with duration of bisphosphonate use (risk was elevated 10-fold within the first 2 years of use and 50-fold with longer use), but fell after discontinuation: A 70% reduction in risk was observed for each year after last use, regardless of duration of prior use.
Schilcher J et al. Bisphosphonate use and atypical fractures of the femoral shaft. N Engl J Med 2011 May 5; 364:1728.
Comment
These findings clarify that, although prevalence of bisphosphonate use is high among women who experience atypical fractures, absolute risk for such fractures is small. Given the well-documented ability of bisphosphonates to prevent osteoporotic fractures, the benefits of this drug class substantially outweigh its risks — provided that use is limited to those patients who meet criteria for prescription therapy. The rapid decline in risk for atypical fractures after bisphosphonate discontinuation supports recommendations for intermittent use (JW Womens Health Aug 12 2010).