Femoroacetabular Impingement (FAI) is a condition affecting the hip joint and is characterized by abnormal contact between the femoral head (hip ball) and the rim of the acetabulum (hip socket), which leads to damage to the articular cartilage (lining or gristle) in the acetabulum, or to the labrum of the hip, or both. The labrum is a ring of cartilage that surrounds the acetabulum and looks very much like the meniscus of a knee joint, although its function is different.
Damage to the labrum and/or articular cartilage will likely cause pain. An abnormality in the shape of the femoral head or acetabulum, or both, may cause FAI. Activities that involve recurrent hip motion can increase the frequency of this abnormal contact, such as kicking sports.
FAI generally presents in three forms:
- Pincer – This type of impingement occurs because extra bone extends out over the normal rim of the hip socket, known as the acetabulum. The surrounding tissue, called the labrum, also can be injured or crushed under the prominent rim of the hip socket.
- Cam – In cam impingement, the ball portion of the hip bone (called the femoral head) is not round, so it cannot rotate smoothly inside the hip socket. This “bump” on the edge of the hip bone can grind and damage the cartilage inside.
- Combined – With combined impingement, both pincer and cam types are present.
FAI can affect all age groups from the early teens and throughout adult life and is being increasingly recognized as a factor that may predispose patients to osteoarthritis of the hip. It is felt by many that without early intervention surgery, there is a high likelihood of developing osteoarthritis with the subsequent requirement for either a hip replacement or other major hip operation. Hip arthroscopy can be used to reshape the femoral head and socket to prevent impingement, and aims to protect the hip from developing osteoarthritis, in addition to relieving current symptoms.
When symptoms develop, it usually indicates that there is damage to the cartilage or labrum and the disease is likely to progress. Symptoms may include pain, stiffness and limping.
Because athletically active 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.
People with FAI usually have pain in the groin area, although the pain sometimes may be more toward the outside of the hip. Sharp stabbing pain may occur with turning, twisting and squatting, but sometimes, it is just a dull ache.