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.

Anatomy

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 (hyaline) 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.

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

Description

In FAI, 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 breakdown of articular cartilage (osteoarthritis). 

Types of FAI

There are three types of FAI: pincer, cam, and combined impingement.

• Pincer - This type of impingement occurs because extra bone extends out over the normal rim of the acetabulum (socket). 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 just means that both the pincer and cam types are present.

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

Cause

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 progress. 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.

Risk Factors

A number of risk factors have been associated with the development of femoroacetabular impingement including:

• Certain athletes, such as football players, weight lifters, and hockey players
• Heavy labourers
• Repetitive hip flexion
• Congenital dislocation of the hip
• Anatomical abnormalities of the femoral head or angular change in the neck or head of the femur
• Hip trauma, including fracture malunion 
• Inflammatory arthritis
• Perthes disease – a childhood hip condition where the blood supply to the head (ball) of the femur is interrupted or impaired leading to bone breakdown and collapse, with subsequent change in shape of the head.

Symptoms

The most common symptoms of FAI include:

• Pain – typically groin pain with activity, though pain may be felt in the front, side or back/buttock region of the hip, and is variously described as a dull ache or sharp pain (more with turning, twisting, and squatting).  Pain is often worse after prolonged sitting or walking.
• Stiffness – there is restricted range of motion.
• Limping.

 Diagnosis

 The diagnosis of FAI is made with a thorough history and physical examination, combined with a number of imaging studies, which may include Xrays, CT scans and MRI scans.

Treatment

Nonsurgical (Conservative) Treatment

Activity modification - Simply changing your daily routine and avoiding activities that cause symptoms may be sufficient.

Non-steroidal anti-inflammatory medications - Drugs 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.

Injection of steroid and local anaesthetic into the joint – this can be both diagnostic (short-term pain relief) as well as therapeutic.

Surgical Treatment

If tests show joint damage caused by FAI and your pain is not relieved by nonsurgical treatment, surgery may be discussed or offered.

Arthroscopy of the Hip

Many FAI problems can be treated with arthroscopic surgery, though this operation should not be undertaken if any arthritis or chondral (joint surface) damage is noted on the imaging studies. 

Hip arthroscopy is a surgical procedure in which an arthroscope (a small fibre-optic camera) is inserted into the hip joint to assess and repair damage to the hip. Hip arthroscopy is performed in a hospital operating room.  It is performed using small incisions and thin instruments. 

A number of options for dealing with specific problems are possible, including:

• Labral/Cartilage Debridement – this involves removal of torn, frayed or unstable labrum or articular cartilage.
• FAI Decompression – This involves removing the bony prominences and bumps on the femoral head or acetabulum to restore more normal shape and to prevent impingement.
• Microfracture – This involves drilling multiple small holes into any exposed areas of bare bone where the joint surface cartilage is absent with the hope of promoting new cartilage formation

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