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Atypical Femur Fractures (AFFs)

What is an AFF?

The AFF task force defined an AFF as a:


  1. A fracture of the femur (thigh bone) that occurs along the femur shaft below the hip and above the knee;

  2. Occurs following no or minimal trauma such as a fall from standing height. If your femur was fractured in a car accident or a sporting accident, then that would be high trauma and would not count as an AFF;

  3. Has a specific appearance on x-rays or CT imaging. In order to be diagnosed with an AFF, a type of x-ray will need to be done and reviewed by a doctor with experience in identifying the characteristics of an AFF. The types of medical imaging that would be done include:

  • An x-ray of the entire length of the femur from the knee to the hip

  • A CT scan of the entire femur from the knee to the hip

  • A total body nuclear bone scan

  • Can be complete or incomplete.

Complete AFF: A complete AFF has a break in the bone that extends all the way through the femur bone and is almost always unable to support any weight. These are most often diagnosed after a low trauma fall, or a quick pivot or some movement that breaks the bone all the way through. Once the bone is broken, it will need to be fixed with emergency surgery.


Incomplete AFF: Some AFFs are found on x-rays or other types of medical imaging before the femur bone breaks completely. An Incomplete fracture involves only the outer side of the femur bone, so that the break can be seen by x-ray or CT scan on the outer side of the femur bone but does not go all the way through the bone. These incomplete AFFs can still support weight but are not stable and physical activity should be limited.

What Makes It 'A-Typical'

The ASBMR Task Force outlined some unique features of an AFF which include:

  1. Their appearance on x-rays. Similar to a piece of chalk breaking in two, AFFs look like one clean break, with no little pieces of bone around it. This is why medical imaging is required in order to make a clear diagnosis.

  2. Are often associated with symptoms such as dull or aching pain/weakness in the groin or thigh area. These symptoms are usually present prior to a diagnosis of an AFF for weeks or months.

  3. AFFs often occur bilaterally, on both femurs. So, if you have been diagnosed with an AFF on one femur, it is important to get imaging on the other femur to ensure there isn’t the beginning of another fracture there.

Who is at Risk for an AFF?

As researchers are still trying to determine what the causes of AFFs are, we are still studying who is at risk for AFFs. Typically, AFFs occur:

  1. More frequently in women but they have been seen in men.

  2. More frequently in post-menopausal women, but they have been diagnosed in pre-menopausal women as well.

  3. More frequently in people who have been taking a type of medication used to treat osteoporosis, called bisphosphonates, but have been reported in people who have never taken bisphosphonates.

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