An atypical femur fracture (AFF) is called “atypical” because of the location and condition of the break. AFFs start as a weakening of the outer rim of the femur (thigh bone) 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 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 over many weeks to months— typically aching pains in the groin or thigh. If nothing is done about the early warning signs, the crack continues to grow and eventually the thigh bone breaks in two!
How are osteoporosis drugs related to AFF?
AFFs have been reported in people using certain osteoporosis (OP) drugs that reduce bone turnover. The list includes alendronate (Fosamax), risedronate (Actonel, Atelvia), ibandronate (Boniva), zoledronate (Reclast), and denosumab (Prolia). Although some people get an AFF without ever taking one of these OP drugs, there are signs that long term use of these drugs is a major cause of the problem. In nearly 85% of AFF cases, an OP drug was being used, usually for longer than 4 years. Also, the AFF risk seems to double for every extra year of OP drug use. However, when people stop using the OP 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 OP drug.
What should you do?
For women at high risk of having an osteoporotic fracture, there is a net benefit of using an OP drug. You should speak with your doctor about a “drug holiday” after 4-5 years of treatment with a bisphosphonate (drug holidays are not recommended with Prolia).
For woman 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 women 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 a health care provider.
How do you reduce your risks from treatments?
In almost all of the reported AFF cases, the patients took the OP drug for four or more years. Because of the strong link to long term use, the FDA has said that OP 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 continue.