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Atypical Femur Fracture

An atypical femur fracture (AFF) is called “atypical” because of the location and condition of the fracture. AFFs start as a weakening of the outer rim of the femur below the hip area. The tiny crack that occurs is a kind of stress fracture, but unlike stress fractures in people who overdo exercise training, this fracture occurs with regular life activities. An AFF is also different from more common osteoporosis fractures that happen after a single injury – like a fall; AFFs develop slowly from repeated, normal activities. In about 2 of the 3 people who get an AFF, there are warning signals that occur over many weeks to months before the bone breaks. If nothing is done about the early warning signs, the crack continues to grow and eventually the thigh bone breaks in two.

The warning sign of AFF is an aching pain in the groin or thigh. 

How are osteoporosis drugs related to atypical femur fractures?

AFFs have been reported in people using certain osteoporosis drugs that are antiresorptive, reducing bone turnover. The list includes alendronate (Fosamax®), risedronate (Actonel®, Atelvia®), ibandronate (Boniva®), zoledronate (Reclast®, Zometa®) and denosumab (Prolia®).  Although some people get an AFF without ever taking one of these drugs, there are concerns that long term use of antiresorptives is a major cause of the fracture. In nearly 85% of AFF cases, an antiresorptive drug was being used, usually for longer than 4 years. Also, the AFF risk seems to double for every extra year of antiresorptive drug use. However, when people stop using the drug, the risk is cut in half for each following year.

In particular, Asian women seem to be at higher risk of an AFF when they take an antiresorptive drug.

Should I worry about atypical femur fractures if I take osteoporosis drugs?

For individuals at high risk of having an osteoporotic fracture, there is a net benefit from using an osteoporosis drug.  Speak with your healthcare provider about a “drug holiday” after 3-4 years of treatment with a bisphosphonate (drug holidays are not recommended with Prolia®).

For individuals at low risk of having an osteoporotic fracture, harm is likely to outweigh benefit. This is because AFFs typically occur in younger, healthy women who are not likely to break a bone from osteoporosis in the near future.  

The biggest challenge is for individuals who are at moderate risk of having an osteoporotic fracture.  Some might benefit from therapy and some may not. There are many factors that need to be weighed and are best discussed with your healthcare provider.

How do I reduce my risks from treatments?

In almost all of the reported AFF cases, the patients took the osteoporosis drug for four or more years. Because of the strong link to long term use, the FDA has said that antiresorptive drugs should not be taken for more than 4-5 years, unless there is a strong reason to continue. Anyone at high risk of breaking a bone should probably continue.

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