Histological finding of atypical subtrochanteric fracture after long-term alendronate therapy

Drug therapy for osteoporosis is widely accepted. Bisphosphonates in particular significantly inhibit bone resorption by suppressing osteoclast activity and increasing bone density [1-3]. Alendronate is one of these bisphosphonates; it was approved in the United States in the 1990s and is commonly prescribed worldwide [1, 4, 5]. Clinical trials have shown its effectiveness in the treatment of fractures related to postmenopausal osteoporosis [6]. However, some recent reports have described unusual subtrochanteric or femoral shaft fractures following long-term alendronate therapy [4, 7-13]. Although no causal relationship between long-term alendronate treatment and these atypical stress fractures has been established, some reports suggest that the severe suppression of bone turnover by alendronate may lead to accumulated microdamage to the bone that subsequently results in complete fracture [4, 12].