Femoroacetabular Impingement (FAI)

(AKA: Femoral Acetabular Impingement)

What is it?

Femoroacetabular impingement is where there is too much friction in the hip joint from bony irregularities. The femoral head and acetabulum rub creating damage to the hip joint. The damage may occur to the articular cartilage (smooth white surface of the ball
or socket) or the labral tissue with normal use.

This FAI impingement generally occurs as two forms Cam and Pincer. The Cam form (Cam comes from the Dutch word meaning "cog") describes the femoral head and neck relationship as aspherical or not perfectly round. This loss of roundness creates abnormal contact between the surfaces. The Pincer form describes the situation where the socket or acetabulum has too much coverage of the socket and results in the labral cartilage at the edge of the socket and the anterior femoral head-neck junction. The Pincer form of the impingement is typically secondary to a turning back of the socket, or a socket that is too deep. Most of the time, the Cam and Pincer forms exist together.

This problem can be associated with cartilage damage, labral tears, early hip arthritis, hyperlaxity, sports hernias, and low back pain. It is common in high level athletes, but also occurs in active individuals.

How is it diagnosed?

Most patients may be diagnosed with a good history, physical exam, and plain x-ray films. A patient's history will generally involve complaints of hip pain and loss of hip motion, and the physical exam will generally confirm the patient's history and eliminate other causes of pain. The x-rays are used to determine the shape of the ball and socket as well as assess the amount of joint space arthritis.

Often an MRI of the hip is used to confirm a labral tear or damage to the joint surface. The MRI is most helpful in eliminating certain causes of non FAI hip pain including avascular necrosis (dead bone) and tumors.

What studies should my doctor order?

AP Pelvis and a Hip x-rays are sufficient. As the x-ray films are the most important
part of the diagnosis, they should be no older than six months and of good quality.
An MRI should be ordered as a left or right hip study with intraarticular gadolinium (contrast dye in the joint) and a pain test. The pain test typically involves placing a
local anesthetic inside the hip joint with the contrast dye. Using the pain test helps
assess whether the pain is coming from inside the hip joint.

Can back pain be a sign of FAI?

Yes. Patients with FAI may complain of low back pain localized to the sacroiliac joint, the buttock, or greater side of the hip. FAI pain typically does not go beyond the level of the knee.

Why does it occur?

No one knows if FAI is a condition that begins at birth or develops during periods of growth. It is most likely a combination.

How did I get it?

Some experts believe that significant athletic activity before skeletal maturity increases the risk of, but no one truly knows. Significant contact sports (i.e., football) are associated with Cam impingement.

Do I have arthritis if I have FAI?

Both plain film x-rays and MRI scans are an incomplete view of the cartilage inside
the hip joint. It is possible and common to have good joint space on plain x-ray films
and no signs of arthritis on MRI and still have significant loss of cartilage within the hip.

Do I have FAI if my hip MRI was read as "Normal"?

At times, an MRI will be read as "Normal" but the clinical history, physical exam, and
plain x-ray films indicate FAI. In this situation, further investigation with an arthroscopic surgery may be needed.

What is an Alpha angle?

The Alpha angle refers to a measurement taken of the hip ball (femoral head and neck junction) to determine how much Cam impingement exists. The larger the Alpha angle, the larger the impingement lesion. The Alpha angle is most accurate when obtained from a special MRI scan that controls for hip rotation, but is not essential to the diagnosis.

My doctor recommended a CT scan of my hip to evaluate for FAI, should I follow this recommendation?

A CT or CAT scan is often helpful in understanding the anatomy of the bones of the hip joint, but not essential to the diagnosis.

My doctor recommended an MRI with IV contrast instead of contrast injected in the hip joint (MRI Arthrogram) to evaluate for FAI, should I follow this recommendation?

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My diagnosis was made after many years of hip pain, is that common?

This condition is very new. Many physicians have heard of a hip labral tear but have not heard these types of impingement.

I've been treated for a labral tear with a hip arthroscopy. Could I have FAI, too?

Hip labral tears are associated with FAI. If you have had your labral tear treated and are still having pain, you may have residual FAI. This residual FAI may accelerate the loss of hip cartilage. Labral debridement is not the same as labral repair.

I don't have any pain, what should I do?

Some patients with FAI complain of stiffness and loss of hip range of motion without any significant pain. Progressive loss of motion in the hip can be associated with ongoing impingement.

My doctor says that FAI doesn't exist, why?

Currently, three different opinions exist regarding FAI. The first is that all hip problems are generally mild and should be managed with nonoperative choices such as injections, therapy or rest. If there is severe hip arthritis, a total hip replacement is considered. The second is that hip problems often involve labral tears and that these tears can be treated by cutting out the torn tissue usually with an arthroscopy. The third is that hip problems often involve labral tears and that these tears are secondary to the labrum getting caught by friction between the ball and socket, the condition of FAI. This third approach often leads to surgical treatment of the bone and soft tissue problems of FAI.

What type of doctor can treat it?

If one has a diagnosis of hip impingement or suspects, one should be evaluated by an orthopaedic hip specialist. Your physician should have experience with either open surgical hip dislocation or hip arthroscopy.

What are my treatment options?

Nonoperative management of FAI is possible, but it involves a change to less activity and a commitment to maintaining hip strength.

Operative management may be addressed via hip arthroscopy or open surgery. In hip arthroscopy, the hip is distracted and an arthroscope is used to make an assessment of the hip joint and treat damage that is found through two to four 1 cm incisions. Often, all of the components of FAI such as the labral tear, damaged cartilage, and friction between the ball and socket can be treated through the arthroscope. Repair of a torn labrum as well as stimulating new cartilage growth (microfracture) are often possible with the arthroscopic approach. A hip arthroscopy involving labral debridement (no repair) and no bony decompression usually takes less than one hour. A hip arthroscopy involving labral/cartilage repair and FAI decompression may take between two and four hours, depending on the amount of work performed.

The open surgical hip dislocation involves an incision (approximately 7 to 10 inches), an osteotomy or bone cutting of the upper thigh bone, and dislocation of the ball from the socket exposing all parts of the joint. This exposure allows treatment of labral tears and abnormal contact between the ball and socket. The open approach can typically be done in a few hours. The open approach is not generally recommended in older patients.
Recovery time from most FAI surgical procedures is about four months to full, unrestricted activity. Your postoperative activity level will depend on your surgeon's recommendation, the type of surgery performed, and the condition of the hip joint at the time of surgery.

What are the main risks?

Complications are uncommon but include the following:

DVT (blood clot)
Infection
Femoral neck fracture
AVN of the femoral head (dead bone)
Nerve injury (Sciatic, LFCN, Pudendal)
Nonunion (open surgical dislocation only)
Scarring/Adhesions

How long can I wait before seeking treatment?

Typically, FAI that produces symptoms for at least six months should be evaluated for surgical treatment. A longer wait may compromise the cartilage of the hip.

Can I be treated with an injection of medicine or good physical therapy?

Generally, this is a chronic condition that does not typically respond to hip injections or physical therapy over the long term.

Can I just wait a few years and have a total hip replacement?

Yes. The postoperative rehabilitation of a total hip replacement is significantly less than a procedure; however, the lifespan of the replacement hip is shorter in younger patients.