Femoroacetabular Impingement (FAI)

Understanding Hip Anatomy:

The hip is a ball and socket joint. The socket is formed by the acetabulum (part of the pelvic bone), and the ball is formed by the femoral head at the top of the femur (thighbone). The surfaces of the ball and socket are covered by smooth articular cartilage that allows the joint to move easily without friction. The outer portion of the socket (acetabulum) is lined with fibrocartilage ring called the labrum. The labrum acts as a “gasket” to help provide stability to the joint.

What is Femoroacetabular Impingement (FAI)?

Femoroacetabular Impingement (FAI) occurs when the ball (femoral head) and socket (acetabulum) rub abnormally together causing damage to the hip joint, including the articular cartilage or the fibrocartilage (labrum).

FAI generally occurs in the form of a CAM or PINCER:


Cam Impingement: refers to a femoral headball that is out-of-round with too much bone. It is more common in men.

Pincer Impingement: refers to an acetabulum (cup) that is too deep and overhangs the femoral head. It is more common in women.

Most hips with FAI have elements of both cam and pincer impingement.

Labral Tears: Fraying or tearing of the fibrocartilage “gasket” in the hip joint.

Hip Dysplasia: A disorder where the cup of the hip joint is too shallow. This may lead to hip instability or further damage to the labrum.

Osteoarthritis (OA): Joint disease caused from cartilage loss due to aging joints, injury, and obesity. OA symptoms include pain and stiffness. If you are overweight, weight loss may improve OA symptoms.

Why does the hip labrum tear?

When impingement is present, the labrum (bumper of tissue around the hip socket) around the hip joint gets pinched. During activities such as running, playing basketball, skiing, yoga or dancing, repetitive trauma to the labrum between the cam or pincer lesions may cause a tear to develop. Once the labrum tears, it does not function optimally and can cause pain that is often felt in the groin or at the top of the hip.

What are the symptoms?

  • Groin pain
  • Difficulty putting on shoes/socks,
  • Difficulty getting in and out of a car
  • Locking, catching, clicking in the hip

How is it diagnosed?

Examination of the hip by an orthopedic hip specialist, x-rays and sometimes MRI are used to look for FAI deformity and labral tears.

How is Femoroacetabular Impingement (FAI) treated?

Your surgeon will discuss whether hip arthroscopy is right for you.  Learn more about hip arthroscopy on our dedicated page.

Also see...