Hip Impingement (Femoroacetabular Impingement, FAI)

Femoroacetabular impingement (FAI) of the hip, also known as hip impingement, occurs when extra bone forms along one or both sides of the hip joint.

The hip joint is made up of the ball of the femur bone and the acetabulum (socket) of the pelvis. The extra bone causes the ball and socket to have an irregular shape during motion. The pinching and repetitive friction can cause pain and damage to the joint over time.

Types of FAI

Impingement can be caused by bone on the neck of the femur (CAM Lesion), edge of the socket (Pincer Lesion) or both.

• CAM: In CAM-type impingement, a bony bump is present at the connection of the head and neck of the femur. This means that the femoral head is not perfectly round. Therefore, the socket cannot rotate smoothly around an aspherical ball. Mismatch between the ball and socket results in impingement during certain movements including flexing and rotating the hip. This can cause wear to the cartilage and tearing of the labrum inside the hip joint.
• Pincer: In Pincer-type impingement, extra bone forms along the outside rim of the acetabulum (socket). The labrum is a ring of thick cartilage that is also on the rim of the socket. During pincer impingement, the labrum can be pinched up against the femur during activity and motion, causing crushing and tearing.
• Mixed: In mixed-type impingement, both CAM and Pincer are present. This is the most common type.

Causes of Hip Impingement

The exact cause of hip impingement is not clear and is likely multifactorial. Because cam lesions are adjacent to one of the hip growth plates, it is thought that the body forms extra bone in this area in order to protect the growth plate during development. There also appears to be a genetic component to hip impingement.

Symptoms of FAI

The most common symptom is groin pain. The pain may be worse with squatting or activities requiring deep hip flexion. Pain may also worsen with longer periods of sitting or standing, and with walking or running. Not everyone experiences pain in the same location, and some patients may feel pain more on the outside or back of the hip. Pain coming from inside the hip joint may refer to other areas, such as the knee or lower back.

Isolated low back pain, numbness and pain that radiates below the knee are unlikely to be caused by hip impingement.

Some patients may experience a clicking or popping sensation in the front of the hip. This can be a sign of a torn labrum or a tight hip flexor muscle.

The symptoms of hip impingement may come and go. In fact, many patients (including active patients and high level athletes) have signs of hip impingement on their x-rays but do not have any symptoms or pain. Patients who are athletic or physically active do tend to have symptoms earlier than those who are not. Only symptomatic FAI needs to be treated, and some people never develop symptoms. When symptoms do present, it is typically a sign of damage occurring inside the hip joint such as cartilage injury or labral tear.

Diagnosis of Hip Impingement

Hip impingement is usually diagnosed with specific hip X-rays and a physical exam. X-rays must be taken at specific angles and positions. Your doctor will then make specialized measurements on your x-rays to identify whether or not impingement is present. X-rays will also show if there are other important structural abnormalities such as dysplasia (shallow hip socket) or retroversion (when the socket is angled posteriorly).

If your doctor suspects impingement, and MRI of the hip joint is the next step. This scan shows whether the labrum or hip cartilage has been damaged. An MRI shows a lot of detail about the health of the hip joint and can also identify early signs of arthritis. A lot of detail can be seen on an MRI about the health of your hip joint, including early signs of arthritis. Your doctor may also order a CT scan to look at the three dimensional anatomy of your bones.

Hip Impingement (FAI) Treatment

More than half of patients with hip impingement get better with nonsurgical treatment, including:

• A period of rest and avoiding activities that cause pain
• Over-the-counter pain medication including ibuprofen, acetaminophen or other anti-inflammatories
• Physical therapy with a therapist who is experienced in treating hip impingement
• Cortisone injection, which is more often used when arthritis is present.

If conservative treatment fails, we may recommend surgery. Prior to surgery, we usually recommend an injection of numbing medication inside the hip joint to confirm that the hip impingement is the source of pain. This is especially important in patients who do not have typical symptoms of FAI.

Surgery is done arthroscopically with a camera through several small one-inch incisions. The procedure usually lasts two to three hours, and patients go home the same day. During surgery, we inspect the joint and use specialized instruments to reshape the bone where it is impinging. If the labrum is torn and repairable, this will also be fixed during the surgery. Physical therapy after surgery is extremely important to your recovery. It usually takes about four to six months to fully recover from a hip arthroscopy.

Long-Term Hip Impingement Treatment Outcomes

The goal of hip impingement treatment is to control pain and prevent further joint damage. Treatment cannot correct damage that has already been done, and it cannot guarantee that damage will not continue to occur.

Hip impingement research and treatment continue to change at a rapid rate. Treatments continue to evolve, and we are always looking at new techniques. The long-term outcomes and progression of joint damage is a topic that is currently being heavily studied in orthopedic research.