FAI or Femoroacetabular Impingement occurs when either the ball or the socket are abnormally formed.

The hip joint is a type of ball and socket joint which is made of the femoral head (the top of the thigh bone which is shaped like a ball) and the acetabulum (part of the pelvis which forms a socket for the ball to sit in).

This results in the ball and socket rubbing abnormally against each other. This causes the hip joint to wear out, causing damage to structures that are important to the proper function of the hip such as:

FAI is a common condition, affecting 25% of people and is one of the most common causes of hip arthritis.

There are 2 types of FAI.

  • CAM impingement. The bone abnormality is located on the ball.
  • PINCER impingement. The bone abnormality is located on the socket.

Cam lesion in FAI Femoroacetabular impingement

Symptoms of FAI

If you have FAI, you will have discomfort in your groin. Sometimes the pain can radiate to your lower back or front of you hip.

Initially, the pain may only be felt whilst playing sport.

With time, you may feel pain with any movement that brings your knees towards your chest, such as:

  • sitting in low chairs
  • getting up from chairs
  • driving
  • putting on your socks and shoes
  • picking things off the ground
  • climbing stairs

Causes of FAI

25% of people have femoroacetabular impingement.

FAI is something that develops when you are growing during your teenage years.

Although it hasn’t been confirmed yet, it is probably genetic, and something that often is common between family members.

It may also develop due to the way that your growth plate may develop over time. Your growth plate is where the bone grows during childhood and teenage years.

Most people don’t know they have FAI until it has caused damage to the hip joint.

It is important to see a doctor as soon as you can if you have groin or hip pain. A simple X-ray can often diagnose the problem.

FAI - CAM impingement


Investigations for FAI

A well trained doctor can usually suspect FAI from your symptoms and an examination of your hip.

A number of investigations can help in the diagnosis of a labral tear:

  • Xray. Specialised X-rays can help look at the shape of your hips. A standard xray of your hip and pelvis is not enough, as it often misses the abnormal hip shape in FAI.
  • CT scan with 3D reconstruction. This is an excellent test for diagnosing FAI and shows the 3D anatomy of your hip. It helps plan the operation by showing the exact location and amount of bone that needs to be removed.
  • MRI scan. Is the best test to show a labral tear which is commonly found in association with FAI. However, labral tears can also be missed by an MRI and sometimes a diagnostic hip injection is needed to prove that your hip/groin pain is coming from your hip joint.

Treatment for FAI

Femoroacetabular impingement can be treated with hip arthroscopy.

During the procedure, the damage in your hip joint can be assessed and treated.

There are many structures in your hip that can be damaged due to FAI.

  • Ligamentum Teres Tears. These tears can be trimmed and stabilised. The inflammation can be removed.
  • Labral Tears. These can be repaired with suture anchors.
  • Cartilage damage. The unstable cartilage can be removed and the underlying bone can undergo a process called microfracturing – which encourages new cartilage to reform. However, this cartilage – called fibrocartilage, is not as good as your original cartilage – called hyaline cartilage. It is much better not to have cartilage damage, as there is no technology available to give you back your original cartilage – including stem cell therapy. Hopefully, one day, stem cell therapy may work, but current techniques have not been shown to work.
  • Pincer Impingement. These bone spurs can be removed with specialised burrs.
  • CAM Impingement. These bone bumps can be removed so that your hip movement is regained, and less damage is done to your hip in the future. Thereby improving your symptoms and making your hip last longer without the wear and tear caused by the CAM or Pincer Impingement. There is now strong evidence that treatment CAM impingement and labral tears have better outcomes than physiotherapy alone. The best outcome is when good surgery is combined with good physiotherapy, and the hip joint does not have too much cartilage damage.
  • Femoral Cysts. These can be removed.



Prevention of damage from FAI

Certain Sports can lead to damage of the hip due to FAI. Although 25% of people have FAI, not all of those people will go on to develop cartilage damage, pain and arthritis.

It all depends on how much the bone bumps grind into the hip joint.

Certain sports involve a lot of hip joint movement and grind the bump into the hip joint. These sports involve a lot of twisting and hip flexion.

  • AFL football
  • hockey
  • netball
  • athletics
  • dancing
  • swimming
  • rugby

If you play sports and have hip or groin pain, you should see your doctor as soon as possible as you may have FAI.

Everyone has a different natural rotation of their hip and it is important to exercise using that natural hip rotation.

Running. Some people should run with their feet pointing straight forward, while other people are naturally pigeon-toed or duck-footed. You should run and jog according to what feels right and most natural.

Cycling. If you find that you cycle with your knees pointing outwards rather than straight up and down, it is important that you don’t were bicycle cleats, which will force your hips into internal rotation and potentially damage your hips.

Further Reading and References