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from the American Academy of Orthopaedic Surgeons

Diseases & Conditions



Staying Healthy

Femoroacetabular Impingement

Femoroacetabular impingement (FAI) is a condition in which extra bone grows along one or both of the bones that form the hip joint — giving the bones an irregular shape. Because they do not fit together perfectly, the bones rub against each other during movement. Over time this friction can damage the joint, causing pain and limiting activity.


The hip is a ball-and-socket joint.

  • The socket is formed by the acetabulum, which is part of the large pelvis bone.
  • The ball is the femoral head, which is the upper end of the femur (thighbone).

A slippery tissue called articular cartilage covers the surface of the ball and the socket. It creates a smooth, low friction surface that helps the bones glide easily across each other during movement.

The acetabulum is ringed by strong fibrocartilage called the labrum. The labrum forms a gasket around the socket, creating a tight seal and helping to provide stability to the joint.

normal hip anatomy

In a healthy hip, the femoral head fits perfectly into the acetabulum.


In FAI, the femoral head and/or the acetabulum have bony prominences (bumps) because either:

  • Your hips formed that way at birth
  • There is bone overgrowth, or bone spurs

bone overgrowth — called bone spurs — develop around the femoral head and/or along the acetabulum. This extra bone causes abnormal contact between the hip bones and prevents them from moving smoothly during activity. Over time, this can result in tears of the labrum and the breakdown of articular cartilage (osteoarthritis).

Types of FAI

There are three types of FAI: 

  • Pincer. This type of impingement occurs because extra bone extends out over the normal rim of the acetabulum. The labrum can be crushed under the prominent rim of the acetabulum.
  • Cam. In cam impingement, the femoral head is not round and cannot rotate smoothly inside the acetabulum. A bump forms on the edge of the femoral head that grinds the cartilage inside the acetabulum.
  • Combined. Combined impingement means that both the pincer and cam types are present.
types of femoroacetabular impingement

(Left) Pincer impingement. (Center) Cam impingement. (Right) Combined impingement.


FAI occurs because the hip bones do not form normally during the childhood growing years. It is the deformity of a cam bone spur, pincer bone spur, or both, that leads to joint damage and pain. When the hip bones are shaped abnormally, there is little that can be done to prevent FAI.

It is not known how many people have FAI. Some people may live long, active lives with FAI and never have problems. When symptoms develop, however, it usually indicates that there is damage to the cartilage or labrum and the disease is likely to worsen.

Because athletic people may work the hip joint more vigorously, they may begin to experience pain earlier than those who are less active. However, exercise does not cause FAI.


The most common symptoms of FAI include:

  • Pain
  • Stiffness
  • Limping

Pain often occurs in the groin area, although it may occur toward the outside of the hip. Turning, twisting, and squatting may cause a sharp, stabbing pain. Sometimes, the pain is just a dull ache.

Home Remedies

When symptoms first occur, it is helpful to try to identify an activity or something you may have done that could have caused the pain. You can modify your activities, let your hip rest, and see if the pain will settle down.

Over-the-counter anti-inflammatory medicines, such as ibuprofen and naproxen, may help to relieve the pain.

If your symptoms persist, you will need to see a doctor to determine the exact cause of your pain and provide treatment options. The longer painful symptoms go untreated, the more damage FAI can cause in the hip.

Doctor Examination

During your first appointment, your doctor will discuss your general health and your hip symptoms. They will also examine your hip.

Impingement Test

As part of the physical examination, your doctor will likely conduct the impingement test. For this test, your doctor will bring your knee up toward your chest and then rotate it inward toward your opposite shoulder. If this re-creates your hip pain, the test result is positive for impingement.

hip impingement test

Impingement test.

Reproduced from Armstrong AD, Hubbard MC, eds: Essentials of Musculoskeletal Care, ed 5. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2015.

Imaging Tests

Your doctor may order imaging tests to help determine whether you have FAI.

  • X-rays. X-rays provide good images of bone and will show whether your hip has the abnormally shaped bones present with FAI. X-rays can also show signs of arthritis.
  • Computerized tomography (CT) scans. More detailed than a plain X-ray, CT scans help your doctor see the exact abnormal shape of your hip.
  • Magnetic resonance imaging (MRI) scans. MRI scans provide better images of soft tissue than X-rays. They will help your doctor identify damage to the labrum and articular cartilage. Injecting dye into the joint during the MRI may make the damage show up more clearly.
  • Local anesthetic. Your doctor may also inject a numbing medicine into the hip joint as a diagnostic test. If the numbing medicine provides temporary pain relief, it confirms that FAI is the problem.


Nonsurgical Treatment

Activity changes. Your doctor may first recommend simply changing your daily routine and avoiding activities that cause symptoms.

Nonsteroidal anti-inflammatory drugs (NSAIDs). Medications like ibuprofen can be provided in a prescription-strength form to help reduce pain and inflammation.

Physical therapy. Specific exercises can improve the range of motion in your hip and strengthen the muscles that support the joint. This can relieve some stress on the injured labrum or cartilage.

Surgical Treatment

If tests show joint damage caused by FAI and your pain is not relieved by nonsurgical treatment, your doctor may recommend surgery.

(Left) A cam bump on the femoral head. (Right) After the bump has been shaved down during surgery.

(Left) X-ray shows a cam bump on the femoral head. (Right) After the bump has been shaved down during surgery.

Reproduced from Diaz-Ledezma C, Higuera CA, Parvizi J: Mini-open approach for the treatment of FAI in Sierra RJ, ed: Femoroacetabular Impingement. Rosemont, IL, American Acad of Orthopaedic Surgeons, 2013, pp 81-91.


Many FAI problems can be treated with arthroscopic surgery. Arthroscopic procedures are performed using small incisions and thin instruments. The surgeon uses a small camera, called an arthroscope, to view inside the hip.

During arthroscopy, your surgeon can:

  • Repair or clean out any damage to the labrum and articular cartilage
  • Correct the FAI by trimming the bony rim of the acetabulum and also shaving down the bump on the femoral head

Some severe cases may require an open operation with a larger incision to accomplish this.

hip arthroscopy

(Left) During arthroscopy, your surgeon inserts an arthroscope through a small incision about the size of a buttonhole. (Right) Other instruments are inserted through separate incisions to treat the problem.

Long-Term Outcomes

Surgery can successfully reduce symptoms caused by impingement. Correcting the impingement can prevent future damage to the hip joint. However, not all of the damage can be completely fixed by surgery, especially if treatment has been put off and the damage is severe. It is possible that more problems may develop in the future.

While there is a small chance that surgery might not help, it is currently the best way to treat painful FAI.

Future Developments

As the results of surgery improve, doctors will probably recommend earlier surgery for FAI.

Surgical techniques continue to advance, and some surgeons are using computer-based navigation systems to help plan and guide bone resection (removal) in FAI surgery.

Last Reviewed

April 2024

Contributed and/or Updated by

Jocelyn Ross Witstein, MD, FAAOSMary K. Mulcahey, MD, FAAOSJ.W. Thomas Byrd, MD, FAAOS

Peer-Reviewed by

Stuart J. Fischer, MD, FAAOSRick Wilkerson, DO, FAAOS

AAOS does not endorse any treatments, procedures, products, or physicians referenced herein. This information is provided as an educational service and is not intended to serve as medical advice. Anyone seeking specific orthopaedic advice or assistance should consult his or her orthopaedic surgeon, or locate one in your area through the AAOS Find an Orthopaedist program on this website.