Atypical Femur Fractures

Atypical femur fractures have received increased research and clinician focus over the past several years. The cause of these fractures and who is at risk for these fractures is still not known. Although atypical femur fractures have been described prior to the use of bisphosphonates, femur fractures that are classified with atypical features are occurring in individuals treated with bisphosphonates.

Distinct X-ray Appearance of Atypical Femur Fractures

An atypical femur fracture is quite distinct from a hip fracture that occurs due to underlying osteoporosis. Because the x-ray features of this thigh bone fracture that occurs anywhere between below the hip and the knee are quite different and occurs with no or little trauma, it is called “atypical.” An international expert group under the auspices of the American Society for Bone and Mineral Research established criteria for the diagnosis in 2010.

It’s these atypical features that have the experts baffled. The appearance of these fractures on an x-ray looks similar to a rare genetic disorder called adult hypophosphatasia. In one case report, a woman who had no outward manifestations of this genetic disorder appeared to have the underlying problem turned on by taking bisphosphonates.

Atypical Femur Fracture Risk Low Compared with Risk of an Osteoporotic Fracture

According to systematic hip fracture data collected by the Kaiser group in California, the risk for atypical femur fracture is quite low. However, the risk appears to increase after five years of use of bisphosphonates. Since individuals treated with bisphosphonates are at high risk for fracture, your risk for an osteoporotic fracture still far outweighs the low risk for atypical femur fractures.

Multiple research hypotheses are being investigated in trying to find the cause of these atypical femur fractures. In the meantime, talk with your doctor or healthcare professional about taking a break in your treatment with bisphosphonates if appropriate called a drug holiday.

Other resources:

Shane E. et al. “Atypical Subtrochanteric and Diaphyseal Femoral Fractures: Report of a Task Force of the American Society for Bone and Mineral Research.” Journal of Bone and Mineral Research. 25 (2010): 2267–2294.