Bisphosphonates are used to prevent hip and vertebral fractures in patients with osteoporosis but on rare occasions may paradoxically contribute to atypical femoral fractures (AFF). "Typical" femoral fractures in osteoporosis occur at the weaker femoral neck or intertrochanteric regions. "Atypical" femoral fractures occur in stronger bone areas such as in the sub-trochanteric area or at the femoral diaphysis . A 2013 meta-analysis found that bisphosphonate users have an increased risk of AFF, although the complication is rare and more studies are needed . The FDA recommends using bisphosphonates no longer than 3-5 years, but there is significant controversy regarding the appropriate duration of treatment .
B. Clinical Perspective:
This patient had bilateral AFF, although the left side pathology was initially missed on x-ray reads. The right femur fracture was complete and more obvious, especially given the clinical presentation. The left femur fracture was subtle, with the most noticeable feature being the callous formation.
C. Imaging Perspective:
The American Society of Bone and Mineral Research has established diagnostic features for AFF to help with identification. For all AFF, "the fracture must be located along the femoral diaphysis from just distal to the lesser trochanter to just proximal to the supracondylar flare." In addition, four out of five major features are required:
Major Features Summarized (See ASBMR article  for full major and minor features):
- fall with minimal or no trauma
- transverse fracture starting at lateral cortex
- complete fracture through both cortices or incomplete only through lateral cortex
- noncomminuted or only minimally comminuted
- localized periosteal/endosteal thickening at the fracture site
The patient's fractures were fixed by open reduction and internal fixation with bilateral intramedullary nails. Ibandronate was discontinued.
E. Take Home Message:
In patients with a femoral fracture suggestive of AFF from bisphosphonates, it is important to obtain an x-ray of the contralateral femur to look for hairline fractures, callus formation, or other key features. AFF are "insufficiency fractures" that occur due to normal stresses on abnormally structured bone, so the two femurs may be equally involved due to systemic bisphosphonate therapy. The contralateral femur may show subtle radiographic findings suggestive of AFF that require immediate surgical fixation before the fracture worsens. In addition, stop bisphosphonate therapy.
When in doubt, a nuclear medicine bone scan can be performed to identify a "hot spot" of healing. An MRI can also be done to look for edema.