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Femoral-Acetabular Impingement (FAI)

Hip pain is typically associated with older adults, but everyone from young athletes to “weekend warriors” and even non-athletes can be at risk for developing this hip problem. Femoral-Acetabular Impingement (FAI) is caused when the hip bones do not form normally during the growing years. Abnormal rubbing at the hip joint causes damage to the cartilage and hip pain.

The hip is a ball and socket joint. The socket is formed by part of the pelvic bone (acetabulum), and the ball is formed by the femoral head at the top of the thighbone (femur). The surfaces of the ball and socket are covered by a slippery tissue called articular cartilage, which allows the joint to move without friction. The socket is lined with a strong fibrocartilage ring called the labrum that forms a gasket to create a tight seal and help provide stability to the joint.


  • Pain in the groin or outer thigh
  • Sharp pain when turning, twisting, or squatting
  • The hip may also pop or catch
  • Pain may increase during physical activity, or after periods of prolonged sitting or walking

Three types of FAI:

  • Cam Impingement is caused when the femur’s head grows into a shape that is unevenly rounded and cannot rotate smoothly in the socket. Certain movements can cause the extra bone to catch against the edge of the socket, damaging the cartilage and labrum.
  • Pincer Impingement is caused when extra bone grows along the socket’s rim, or when the socket is not angled properly, allowing the socket and femur to impact abnormally.
  • In many cases, FAI is caused by a combination of cam and pincer types.

Diagnosis and Treatment

Examination of the hip by an orthopedic hip specialist, x-rays, and sometimes an MRI are used to look for FAI deformity and labral tears. Treatment options can include changes in lifestyle that place less stress on the hip, physical therapy, or arthroscopic surgery. During this surgery, a small camera (called an arthroscope) is inserted into the joint and allows for a clear view of the hip ball and socket joint. This allows your orthopedics surgeon to look for the causes of your hip pain. The camera displays pictures onto a screen, and surgical instruments are guided into your hip to repair the joint.