Femoroacetabular Impingement (FAI)

In a healthy hip, the rounded top of thigh bone (femoral head) “plugs into” the hip socket (acetabular socket) in such a way that the femoral head can move smoothly within the socket. The ball and socket are lined with a thin layer of smooth cartilage that cushions and protects the bones, preventing them from rubbing or grinding against each other. The rim of the hip socket is lined with a special ridge of cartilage called the labrum that further helps to secure the femoral head in place inside the hip socket.

Hip impingement or Femoroacetabular Impingement (FAI) occurs when something prevents the smooth, painless, and free movement of the ball-and-socket joint – basically, it is a condition of too much friction in the hip joint, thus creating damage to the hip joint.

The damage can occur to the articular cartilage (smooth white surface of the ball or socket) or the labral cartilage (soft tissue bumper of the socket).

FAI is associated with cartilage damage, labral tears, early hip arthritis, hyperlaxity, sports hernias, and low back pain.

FAI is common in high level athletes, but also occurs in active individuals.

Cause

Hip impingement may be caused by a misshapen femoral head, deformed femoral neck, or a hip socket that covers too much of the femoral head. Over time, repetitive “bumping” or impingement of the femur on the rim of the acetabulum leads to cartilage and labral damage.

People with hip impingement may have been born with a structurally abnormal ball-and-socket joint. In other cases, the hip joint may have become structurally abnormal during development. Repetitive activity involving recurrent movement of the legs beyond the normal range of motion may cause hip impingement, which has been observed in certain athletes (football, baseball, tennis, hockey, dancers, and golfers). An injury may also cause symptoms of hip impingement.

Further, certain conditions, such as Perthes disease and slipped capital femoral epiphysis (SCFE), may cause hip impingement.

FAI - Cam, Pincer, MixedFAI generally occurs as two forms: Cam and Pincer.

The Cam form describes the femoral head and neck relationship as aspherical or not perfectly round. This loss of roundness contributes to abnormal contact between the head and socket.

The Pincer form describes the situation where the socket or acetabulum has too much coverage of the ball or femoral head. This over-coverage typically exists along the front-top rim of the socket (acetabulum) and results in the labral cartilage being “pinched” between the rim of the socket and the anterior femoral head-neck junction. The Pincer form of the impingement is typically secondary to “retroversion”, a turning back of the socket, or “profunda”, a socket that is too deep.

Most of the time, the Cam and Pincer forms exist together.

Signs & Symptoms

In the early stages, there may be no symptoms associated with hip impingement or symptoms may be mild or vague. Some typical symptoms include:

  • Stiffness in the thigh, hip, or groin
  • The inability to flex the hip beyond a right angle
  • Pain in the groin area, particularly after the hip has been flexed (such as after running or jumping or even extended periods sitting down)
  • Pain in the hip, groin, or lower back that can occur at rest as well as during activity

femoro-acetabular-impingement-diagnosisDiagnosis

An accurate diagnosis of hip impingement is crucial since, left un-treated, hip impingement can lead to cartilage damage and osteoarthritis.

Diagnosis begins with a complete medical history and a physical examination. During the physical exam, the range of motion of the hip joint and presence of impingement will be assessed.

Patients who present with symptoms of FAI often complain of pain in the groin after prolonged sitting or walking. Many athletes often describe pain in the groin with deep flexion or rotation of the hip during activity. The pain can be described as a dull ache or a sharp sensation. Occasionally, a popping or clicking in the front of the hip is described. Pain can also be felt along the side of the thigh and in the buttocks. It is important to rule out other causes of hip pain such as the low back or abdomen.

Radiographs of the pelvis are used to confirm the diagnosis of FAI. Often an MRI or CT scan is performed to further assess the cartilage, labrum, and shape of the bones.

Other tests may be required, including:

  • X-rays of the pelvis are used to confirm the diagnosis of FAI
  • Often an MRI or CT scan is performed to further assess the cartilage, labrum, and shape of the bones

Treatment

Non-Surgical Treatment

Treatment of FAI begins with conservative, non-surgical methods. Rest, activity modifications, careful use of anti-inflammatory medications, and a course of physiotherapy are often successful in alleviating symptoms. An injection of the hip joint with anesthetic can also provide some relief as well as diagnostic information in patients with symptoms which are unresponsive to treatment.

Surgical Treatment

In some cases, surgical intervention is recommended.

Such surgery may be minimally invasive (arthroscopic) or open. Arthroscopic treatment is the more common and can correct most impingement deformities. Severe or complicated impingement deformities are best managed as open surgery in order to insure full correction of the deformity.

In some cases, an osteotomy (literally “bone cutting”) procedure can be performed in such a way that it relieves the impingement of the hip joint. By realigning the joint properly, the abnormal contact can be reduced or eliminated.

An abnormally shaped femoral head or hip socket can often be reshaped with osteoplasty or debridement. In such cases, the surgeon can “clean” or “sculpt” the ball-and-socket joint for a smoother fit.

For young, athletic individuals, arthroscopic or open repair of the joint may be appropriate. Arthroscopy is a specialized, minimally invasive procedure to repair the joint. Open surgery is indicated for more severe cases. Both arthroscopic and open procedures can provide excellent clinical results.

After surgical repair, the patient typically undergoes a period of physical rehabilitation that can last three to four months. Most patients resume normal activities after FAI surgery in six weeks, but full recovery may take up to six months.

In some cases, people with hip impingement may need to have a total hip replacement.

The choice of treatment depends in part on the patient’s condition, amount of arthritis in the joint, patient’s age and activity level, and specific preferences.

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