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Femoroacetabular Impingement (FAI)

What is FAI?

The hip is a ball (femur) and socket (acetabulum) joint, which allows for motion in nearly all directions. In hip impingement, or FAI, the structure of the hip is subtly altered, resulting in abnormal motion. The best analogy for FAI is a square peg in a round hole; that is, the ball and socket of the hip do not quite fit together properly, resulting in abnormal mechanics and eventual damage to the joint. Long-standing, untreated FAI may actually be one of the most common causes of osteoarthritis of the hip.

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There are two types of hip impingement: cam and pincer. Cam impingement occurs when the ball of the hip joint is not perfectly round. Pincer impingement occurs when the socket of the hip overhangs and impinges (presses) against the ball. In both cases, the eventual result is labral tears, cartilage damage and hip pain. A Mayo Clinic study recently found that bone abnormalities were present in greater than 85 percent of patients with labral tears, emphasizing the close association between labral tears and FAI.

What are the symptoms of FAI?

People with FAI or hip impingement generally have deep pain in the groin and limited hip rotation. Pain is usually activity related but may also occur when the hip is bent, such as with prolonged sitting. Because the bone changes that occur in FAI often lead to labral tears, the symptoms of FAI and labral tears are very similar.

How is FAI diagnosed?

FAI is usually diagnosed by a detailed examination by your sports medicine physician. Specialized x-rays are also necessary to evaluate the bone structure of the hip. A specialized MRI is used to diagnose labral tears, which often occur in people with FAI. In some patients, a hip injection may be considered to verify the diagnosis of FAI and labral tear and also to treat symptoms.

How is FAI treated?

Treatment of FAI is individualized, based on symptoms and imaging (x-ray and MRI). Some people with mild symptoms and minor bone changes respond well to physical therapy and activity modification. However, when FAI is severe or in highly active individuals, surgical treatment may be required. In most cases of FAI, the bone of the hip can be recontoured arthroscopically, recreating a normal joint surface and improving symptoms and flexibility. Labral tears are often treated with the same procedure.

Because treatment of FAI is very specialized, it is important that you see a sports medicine physician who is experienced in hip arthroscopy and the treatment of athletic hip injuries and FAI.