Researchers report that long-term use of its Fosamax osteoporosis drug is associated with unusual fractures of the thigh bone, HealthDay writes. The fractures were low-energy fractures, meaning that they all occurred from a fall from standing height or less, and the bone cracks were in an unusual horizontal pattern. About one-third of women with these types of fractures were on long-term therapy to prevent osteoporosis, and of these women, two-thirds were taking Fosamax for an average of more than seven years.

Fifteen women were included in the analysis. The average time on Fosamax was 5.4 years before they experienced the unusual femur fracture. Of these 15, 10 women had similar, atypical fractures. These women had been taking Fosamax for an average of 7.3 years, while the remaining five had only been on the drug for an average of 2.8 years. “These were peculiar fractures that would occur when the women were basically doing nothing,” Joseph Lane, chief of metabolic bone disease at the Hospital for Special Surgery at Weill Cornell Medical College and the lead author, tells HealthDay.

“Our results provide further evidence of a potential link between alendronate use and low-energy fractures of the femur,” the authors wrote in a letter reporting their findings, which is published in the March 20 issue of the New England Journal of Medicine. But, the authors acknowledge the limitations of their retrospective analysis and suggest that these findings need to be confirmed in a prospective study.

Merck spokesman Ron Rogers tells HealthDay that “Fosamax has not been associated with an increased risk of fracture at any skeletal site.” He also notes the study didn’t prove a cause and effect relationship between the drug and these unusual fractures, and that the researchers noted that 63 percent of women treated for low-energy fractures weren’t taking bisphosphonates, a class of drugs that includes Fosamax. The drug, by the way, lost patent protection last year.