What is femoro-acetabular impingement (FAI)?
The hip joint is made of the upper end of the thighbone (known as the femoral head and neck) and the hip socket (called the acetabulum). Cartilage, or labrum, lines the rim of the hip socket. Femoro-acetabular impingement (FAI) is a disease of the hip that occurs when the femur head-neck junction touches or squeezes the hip socket during specific types of motion that involve flexion of the hip.
Patients with FAI have an “abnormal relationship” between the femur and hip socket, resulting in increased hip contact from motion. This abnormal relationship may be caused by an abnormal shape of the upper femur (known as a CAM type of impingement) or abnormal shape of the hip socket (known as a PINCER type of impingement). In some cases a combination of these two abnormalities are present.
What causes FAI?
There are many theories for what may cause an abnormal relationship between the femur and hip socket. It can be due to previous childhood diseases such as Legg-Calve-Perthes, slipped capital femoral epiphysis (SCFE), or to the patient’s natural anatomy that results in injury once the hip is stressed in sports.
Who gets FAI?
Femoro-acetabular impingement is likely a result of genetics (which influence how the hip is formed and shaped) and environment (a child’s level and type of physical activity). Some experts believe that significant athletic activity before the body’s skeleton is fully matured increases the risk of FAI, but its exact cause has not been proven.
While it is difficult to prevent hip impingement from occurring, contact sports may make it worse. FAI is common in kids who are involved in a sport or activity where the hip is placed in extremes of motion. Sports that can bring out symptoms of impingement are dance, basketball, swimming, track and volleyball. However, any sport could cause FAI.
Learn more about sports and common orthopedic conditions.