Femoroacetebular Impingement

What is a Femoroacetabular Impingement?

Femoroacetabular impingement (FAI) is a condition where the bones of the hip are abnormally shaped. Because they do not fit together perfectly, the hip bones rub against each other and cause damage to the joint.

Labral Anatomy

The hip is a ball-and-socket joint. The socket is formed by the acetabulum, which is part of the pelvis. The ball is the femoral head, which is the upper end of the femur (thighbone). Articular cartilage lines the joint. It is a smooth, low friction material that covers the surface of the ball and socket, enabling the bones to glide easily across each other. In a healthy hip, the femoral head fits perfectly into the acetabulum.

The acetabulum is ringed by a strong fibrocartilage gasket called the labrum. The labrum creates a tight seal, keeps in the lubricating fluid, and helps to provide stability to the joint.

What is hip impingement?

Impingement usually occurs because the hip does not form as a perfect ball and socket during childhood. Either the ball is not properly round, causing CAM impingement; or the socket has extra bone extending out beyond the normal rim, causing PINCER impingement.  In many cases, there are elements of both cam and pincer impingement present. FAI leads to the cartilage and labrum being pinched or squeezed between the abnormal ball and socket, limiting movement and causing pain. Over time, this action can result in the tearing of the labrum and breakdown of articular cartilage. Eventually, progression of this damage can lead to arthritis of the hip joint.

What are the symptoms of hip impingement?

Many people with the x-ray appearances of FAI never get significant problems, probably because they are able to avoid pushing their hip into positions of impingement. However people with large abnormalities or athletically active people who work the hip joint more vigorously may begin to experience pain earlier than those who are less active. People with impingement usually have pain in the groin area, although it can be felt elsewhere. Sharp stabbing pain may occur with turning, twisting, and squatting, or specific sporting activities, but sometimes, it is just a dull ache. Catching, clicking or popping may indicate a labral tear associated with the impingement. When symptoms first occur, it is helpful to try and identify an activity or something you may have done that could have caused the pain. Sometimes, you can just back off on your activities, let your hip rest, and see if the pain will settle down. Over-the-counter anti-inflammatory medicines (ibuprofen, naproxen) may help.

How is impingement diagnosed?

A diagnosis of impingement is suggested by the pattern of hip pain and limitations. Other problems can mimic hip impingement, including hernia, groin muscle injuries and back problems. An examination will help to exclude these diagnoses.

X-rays:  of your hip will be performed to assess the shape and orientation of the bones.

MRI scan:  will show up labral tears and cartilage damage.

Local anaesthetic:  is usually injected into the hip at the same time as the MRI scan. This is important to figure out if your pain is truly coming from within the hip joint itself.

CT scan:  In some patients, if we are considering surgery, we will perform a 3D CT scan to accurately map the shape and size of the abnormalities we need to remove during surgery. If you have early arthritis, CT is important to ensure you have enough cartilage in the joint to make hip arthroscopy worthwhile.

3D CT scan of hip before and after impingement surgery to remove cam bump (white circle) from femur