Discussion

To the best of our knowledge, this is the first reported case of an atypical femoral fracture in a patient with osteogenesis imperfecta who has been treated with bisphosphonates. The clinical and radiographic presentation is compatible with all 5 major features described by the American Society for Bone and Mineral Research (ASBMR) task force, and 4 of the minor features also (Shane et al. Citation 2010). In particular, the fracture was preceded by thigh pain. Despite the high number of recurrent fractures, the femur was involved only once prior to this most recent episode, but this involved the contralateral femur and was a result of high-energy trauma. The patient started on alendronate therapy and a good response was observed with an increase in bone mineral density of the lumbar spine and femoral neck. In addition, the indices of bone resorption decreased over the same time period. While no typical osteoporotic fractures had occurred since initiation of bisphosphonate, the patient developed an atypical femoral fracture after 3 years of treatment. It is therefore conceivable that the reduction in bone turnover together with the increase in bone stiffness may have avoided typical osteoporotic fractures while favoring the accumulation of microdamage at the point of maximal stress (Pauwels Citation 1948), thus contributing to the development of an insufficiency fracture (Mashiba et al. Citation 2001, Citation 2005).