Abnormal Bone Growth That Causes Friction Within the Hip Joint

Femoroacetabular impingement (FAI) is a condition affecting the femur (thighbone) and acetabulum (hip socket). The top of the femur (femoral head) fits into the acetabulum, forming the ball-and-socket hip joint. FAI occurs when either an abnormal growth on the femoral head or overhanging of the acetabulum causes the two bones to rub against each other in a way that causes pain.

There are two types of FAI: 

  • Cam impingement. In this type, there is a bony deformity on the femoral head that causes it to no longer be round and smooth. Cam impingement is more common in men. 
  • Pincer impingement. With pincer impingement, the acetabulum is not positioned correctly or covers too much of the femoral head.

Though the cause of FAI is not known yet, athletes and younger, active adults are most at risk for the condition. Sports and activities often associated with FAI include soccer, football, baseball, ice hockey, golf, lacrosse, cycling, rowing, deep squatting and ballet.

Symptoms, Diagnosis and Outlook

Femoroacetabular impingement causes pain in the hip or groin, especially when you raise your leg or turn your foot in toward your body. Limitations in range of motion of the hip joint are also a sign of FAI.

Your doctor can diagnose FAI by completing a physical exam and reviewing your medical history. An X-ray scan or a special type of MRI test called an MR arthrogram may also be done to further assess the affected hip.

FAI that is causing pain may be best treated with surgery. Many active adults experience pain relief after surgery. If left untreated, FAI can lead to hip arthritis.

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