Bilateral Low-Energy Simultaneous or Sequential Femoral Fractures in Patients on Long-Term Alendronate Therapy

Background: While alendronate therapy has been shown to decrease the risk of vertebral and femoral neck fractures in postmenopausal osteoporotic patients, recent reports have associated long-term alendronate therapy with unilateral low-energy subtrochanteric and diaphyseal femoral fractures in a small number of patients. To our knowledge, there has been only one report of sequential bilateral femoral fractures in patients on long-term bisphosphonate therapy. Methods: We retrospectively reviewed the case log of the senior author over the last four years to identify patients who presented with a subtrochanteric or diaphyseal femoral fracture after a low-energy mechanism of injury (a fall from standing height or less) and who had been taking alendronate for more than five years. Radiographs were reviewed, and the fracture patterns were recorded. Serum calcium levels were recorded when available. Results: Seven patients who sustained low-energy bilateral subtrochanteric or diaphyseal femoral fractures while on long-term alendronate therapy were identified. One patient presented with simultaneous bilateral diaphyseal fractures, two patients had sequential subtrochanteric fractures, and four patients had impending contralateral subtrochanteric stress fractures noted at the time of the initial fracture. Of the latter four, one patient had a fracture through the stress site and the other three patients had prophylactic stabilization of the site with internal fixation. No patient had discontinued alendronate therapy prior to the second fracture. All patients were women with an average age of sixty-one years, and they had been on alendronate therapy for an average of 8.6 years. All fractures were treated with reamed intramedullary nailing and went on to union at an average of four months. Conclusions: In patients on long-term alendronate therapy who present with a subtrochanteric or diaphyseal femoral fracture, we recommend radiographs of the contralateral femur and consideration of discontinuing alendronate in consultation with an endocrinologist. If a contralateral stress fracture is found, prophylactic fixation should be considered.