2020 Update on bone health

Atypical femur fracture risk and bisphosphonate use

Black DM, Geiger EJ, Eastell R, et al. Atypical femur fracture risk versus fragility fracture prevention with bisphosphonates. N Engl J Med. 2020;383:743-753.

Since their introduction in the 1990s, bisphosphonates have been the mainstay of osteoporosis treatment. This category of medications inhibits osteoclast-mediated resorption and remodeling of bone. Various large, randomized, controlled trials have established the efficacy of bisphosphonates to increase BMD and decrease the risk of hip and vertebral fracture by as much as 40% to 70%.¹³

However, case reports of unusual fragility fractures in the subtrochanteric region and along the femoral diaphysis in patients treated with bisphosphonates started to appear approximately 15 years ago.¹⁴ Since then, concerns and publicity about these atypical fractures have led to substantial declines in bisphosphonate use clinically.

Bisphosphonate preventive benefits versus atypical fracture risk

Black and colleagues reviewed data on women 50 years and older who were enrolled in the Kaiser Permanente health care system in California. The total cohort included slightly more than 1 million women, of which almost 200,000 (17.9%) used bisphosphonates at any point from 2007–2017.

A total of 277 atypical femur fractures occurred. Among bisphosphonate users, there were 1.74 fractures per 10,000 patient-years. Overall, there were almost 59 fractures per 10,000 person-years. The incidence of atypical fractures was highest in women between the ages of 75 and 84 years, and the incidence diminished after age 85. Rates of atypical fractures increased as the duration of bisphosphonate use increased. In addition, rates of atypical fractures decreased with time since bisphosphonate discontinuation.

The rate of atypical fractures in women who had never received bisphosphonate therapy was 0.1 per 10,000 person-years. The number of fractures prevented for each fracture type far outweighed bisphosphonate-associated atypical fractures at all time points along the 10 years of study. In White women, for instance, at 3 years there were 541 clinical fractures prevented and 149 hip fractures prevented, while 2 bisphosphonate-associated atypical fractures occurred, all per 10,000 women.

Interestingly, in the Asian population at the same time point, 330 clinical fractures were prevented and 91 hip fractures were prevented, but 8 atypical fractures of the femur occurred, per 10,000 women. The authors further referenced an earlier Kaiser study that showed that 49% of 142 atypical femur fractures occurred in Asian patients who comprised only 10% of the study population.¹⁵

The authors concluded that the risk of atypical femur fracture increases with longer duration of bisphosphate use and rapidly decreases after bisphosphate discontinuation. Asian women have a higher risk than White women. With bisphosphonate treatment, the absolute risk of atypical femur fracture is very low compared with the reduction in the risk of hip and other fractures.

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