Femoroacetabular impingement

Femoroacetabular impingement (FAI) is a condition of the hip joint in which the femoral head (the ball-shaped end of the femur) and the acetabulum (the cup-shaped socket in the pelvis) do not fit together properly. This can lead to pain and restricted movement in the joint. Normally, the femoral head and acetabulum fit smoothly together, allowing the leg to move in various directions; however, with FAI, they come into premature contact due to an abnormal deformation of one or both structures.

What causes femoroacetabular impingement?

Recent research has shown that cam morphology often develops between the ages of 12 and 16, a period during which the growth plates of the femoral head are not yet closed. Under increased stress on the hip, such as with intensive, high-impact sports and extreme movements (e.g., football), the body may react by producing extra bone at the growth plate to provide additional stability. This can result in a bump or thickening on the femoral head.

It is important to know that this bump or thickening occurs in many people without causing any symptoms. Only a small number of people later develop symptoms associated with femoroacetabular impingement (FAI). Symptoms usually appear in early adulthood, often due to repetitive conflicts between the bump on the femoral head and the acetabulum, for example, during physical activities that place heavy loads on the joint. Symptoms can also appear later if physical activity suddenly increases, such as with work-related strain or the start of intensive sports.

Less is known about pincer morphology, but it often appears to be the result of minor anomalies during pelvic development. There is evidence that genetic factors play a role in the development of both cam and pincer morphology. A family history of hip problems can increase the risk of developing FAI.

There are different types of femoroacetabular impingement, generally classified as cam morphology, pincer morphology, and a mixed form.

Cam morphology: In this type, the femoral head is not perfectly round; instead, it has a bump or thickening. During movement, this bump can rub against the rim of the acetabulum, causing pain. The cam type usually occurs in young adults, especially in intensive athletes who engage in high-impact sports, extreme hip movements, or explosive activities. This type is more common in men.

Pincer morphology: In this type, the acetabulum is overgrown or too deep, causing it to cover too much of the femoral head. This can lead to premature contact with the femoral head and pain during hip movements. The cause of the extra bone formation on the acetabulum is not yet fully understood, but it is often considered an anomaly during pelvic development. This type is more common in women.

Coxa profunda and coxa protrusio: This means the acetabulum is too deep, causing the femur to impinge against the socket. This is a congenital anomaly that is more common in women.

With femoroacetabular impingement (FAI), pain is usually experienced during:

• Deep hip flexion
• Hip rotations
• Impact sports, deep bending movements, and changes of direction
• Walking
• Prolonged sitting
• Squatting
• Cycling using a road bike
• …

With the right treatment and self-care measures, symptoms can often be well managed, and a good quality of active life can be maintained. Our own data show that 84% do not need surgery through exercise therapy. If symptoms persist, an injection may be administered, or surgery may be required.

Several surgical options are available for the treatment of femoroacetabular impingement, depending on the severity of the FAI and the possible presence of osteoarthritis:

• Arthroscopy
• Total hip arthroplasty (if there is also a severe form of osteoarthritis)

We will discuss with you which treatment option is most suitable based on your specific situation and needs.