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.

The improper contact between the ball of the hip joint (femoral head) and the hip socket (acetabulum) leads to pain and potential damage in the hip joint, particularly in the cartilage and the labrum, a ring of soft tissue around the acetabulum that stabilizes the joint.

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

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

Types of FAI

There are three types of femoroacetabular impingement (FAI):

• Cam Impingement: This type of impingement occurs when the femoral head is not perfectly round and has an extra bony bump on the edge of the femoral head. Because the femoral head is not round, it cannot rotate smoothy inside the acetabulum. The femoral head bump jams into the acetabulum during hip flexion or rotation and grinds the cartilage inside the acetabulum.
• Pincer Impingement: This type of impingement occurs because extra bone extends out over the normal rim of the acetabulum, creating a bony “lip” known as a “pincer lesion.” .The labrum can be crushed under the prominent rim of the acetabulum during hip movement.
• Combined Impingement: Combined impingement means that both the pincer and cam deformity are present, leading to a more complex impingement.

Cause of FAI

FAI occurs because the hip bones do not form normally during the childhood growing years. When the hip bones are shaped abnormally, there is little that can be done to prevent FAI.

Some people may live long, active lives with bony 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.

Exercise does not cause FAI. However, active people use the hip joint more vigorously and may begin to experience pain earlier than those who are less active.

Symptoms

Symptoms of FAI include hip or groin pain, stiffness, and a limited range of motion, especially during activities like squatting, bending, or rotating the hip. Over time, repetitive impingement can cause damage to the labrum and cartilage, and lead to early osteoarthritis.

Treatment

Treatment for FAI can range from conservative methods, such as activity modification and physical therapy. However, surgical intervention may be necessary to correct the bony irregularities and prevent further damage, especially if there is significant damage or the condition impacts daily activities and quality of life.