Femoroacetabular Impingement (FAI)

Femoroacetabular impingement (FAI), also called hip impingement, is a condition where the hip joint is not shaped normally. This causes the bones to painfully rub together. This condition can be treated with corticosteroids, nonsteroidal anti-inflammatory drugs (NSAIDs), physical therapy, rest and surgery.


What is femoroacetabular impingement (FAI)?

FAI is an unusually shaped hip joint that causes two bones in the hip to rub together. The pressure causes friction between the top of the femur (thighbone) and acetabulum (part of the pelvis). FAI can limit motion and cause pain.

Without treatment, FAI can damage the cartilage that provides cushioning in the hip. This damage can lead to arthritis, or painful joint deterioration. Some people need surgery to repair the damage. FAI is also called hip impingement.


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How common is femoroacetabular impingement (FAI)?

FAI is a common cause of hip pain in adolescents, adults and athletes of all ages.

Symptoms and Causes

What causes femoroacetabular impingement (FAI)?

The hip joint is a ball-and-socket joint that attaches the femur to the pelvis. People with FAI have an abnormality in the ball (top of the femur) or the socket (groove in the hip bone). The abnormality causes friction during movement and can damage the surrounding cartilage and labrum (cartilage that lines the hip socket).

The abnormalities associated with FAI are usually present at birth. But they can develop later in life, especially during the teenage years. Doctors classify FAI into one of three categories based on the cause:

  • Cam: This type results from a bony growth at the head of the femur. In some cases, physical activity may cause this growth to occur.
  • Pincer: Caused by extra bone growth in the hip socket, this growth often happens during a child’s development.
  • Combined: Both the cam and pincer types of FAI are present.

Physically active people may experience pain from FAI earlier than people who are not as active. But in most cases, exercise does not cause FAI.


What are the symptoms of femoroacetabular impingement (FAI)?

Some people with FAI notice no symptoms. Signs of the condition may appear as damage in the hip worsens. The signs and symptoms of FAI include:

  • Hip pain that worsens during physical activity or long periods of sitting
  • Limping
  • Stiffness in the hip

Diagnosis and Tests

How is femoroacetabular impingement (FAI) diagnosed?

Doctors use several tests to diagnose FAI. Your doctor will ask about your family history and activity levels. To confirm a diagnosis of FAI, your doctor may use:

  • Imaging tests: Tests such as X-rays and MRIs help doctors identify abnormalities and signs of damage in the hip joint.
  • Impingement test: Your doctor brings your knee up to your chest and rotates it toward the opposite shoulder. Someone with FAI will feel the same kind of pain with this movement.
  • Local anesthetic: A doctor identifies FAI by injecting the hip joint with numbing medicine to see if the injection relieves the pain.
  • Physical exam: A physical evaluation helps your doctor assess range of motion, muscle strength and the way you walk to determine if the hip joint works properly.


Management and Treatment

What are the treatments for femoroacetabular impingement (FAI)?

FAI treatment varies according to the person and the severity of the damage. Treatment options for FAI include:

  • Corticosteroids: These drugs reduce inflammation (swelling) in and around the hip joint. Doctors usually deliver this treatment by injection.
  • Nonsteroidal anti-inflammatory drugs (NSAIDs): This type of medicine reduces inflammation and is typically taken in pill form.
  • Physical therapy: Special exercises can help strengthen the joint and improve mobility.
  • Rest: By limiting activity, you can reduce friction in the hip joint.
  • Surgery: Doctors repair the joint with operations including:
    • Arthroscopic hip surgery: In this minimally invasive procedure, a doctor repairs or removes damaged bone or cartilage.
    • Traditional hip surgery: In more severe cases, doctors make a larger incision in an open operation to repair damage.

What are the complications associated with femoroacetabular impingement (FAI)?

Some people with FAI who do not receive treatment develop hip osteoarthritis (breakdown of the cartilage around the hip). This complication can lead to severe pain and limited mobility.


How can you prevent femoroacetabular impingement (FAI)?

Most cases of FAI cannot be prevented. Prompt treatment is important to prevent FAI from causing more damage in the hip.

Who is at risk of developing femoroacetabular impingement (FAI)?

In some cases, people who are physically active have a higher risk of developing FAI.

Outlook / Prognosis

What is the prognosis (outlook) for people with femoroacetabular impingement (FAI)?

Doctors can successfully treat many cases of FAI. Many people who receive treatment for FAI go on to live long and active lives without hip pain.

Living With

When should I see a healthcare provider about femoroacetabular impingement (FAI)?

Contact your healthcare provider if you or your child experiences symptoms of FAI.

What questions should I ask my doctor?

If you have FAI, you may want to ask your doctor:

  • How will FAI affect my daily life?
  • What type of treatment is best for me?
  • What are the risks and benefits of having surgery?
  • What changes do I need to make to my usual activities, and are these changes temporary or permanent?
Medically Reviewed

Last reviewed on 07/02/2019.

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