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.

How common is femoroacetabular impingement (FAI)?

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

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

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