Femoroacetabular Impingement (FAI)


What is FAI?

FAI stands for “femoroacetabular impingement,” or hip impingement for short. FAI occurs when extra bone around the hip bumps up against the labrum and cartilage in the hip joint, or hip socket, resulting in pain and ultimately stiffness and early arthritis.

Symptoms of FAI

FAI can start off with just mild pain in early stages. Most of the pain is felt in the groin area, although it sometimes hurts on the outside or back of the hip. In many cases the pain can progress to severe levels. Untreated FAI can lead to stiffness and early arthritis. Occasionally, labral tears or an inflamed psoas tendon can cause snapping or catching sensations in the hip.

Anatomy of the Hip Joint

The hip joint can be thought of as a ball-and-socket joint. The femoral head is the ball, and the acetabulum is the hip socket. The hip labrum serves as a gasket around the socket to add stability to the hip. Sometimes extra bone grows on either the ball or socket side. This extra bone results in an abnormal shape that not bumps against, or impinges, against other structures in the hip. The result of this can be anywhere from mild pain at first, to a tear of the labrum and damage to the cartilage.

When the extra bone occurs around the femoral head (or the ball), this is known as a cam lesion or or cam deformity, and it causes cam impingement. When it occurs around the acetabulum (socket) it is known as a pincer deformity or a pincer impingement. When it occurs on both areas, it is mixed impingement. Both types of impingement result in similar symptoms, although each causes unique patterns of damage to the cartilage and the labrum.

When impingement occurs, most patients notice restricted, or limited range of motion in the hip. This hip impingement can cause pain in the hip and groin area. It can be difficult to flex the hip joint. It can also cause damage to the articular cartilage of the hip joint. This articular cartilage damage can ultimately lead to hip arthritis, or hip osteoarthritis.

Diagnosis of Hip Impingement

The diagnosis of FAI is made based off a thorough history and physical examination, and imaging tests consisting of x-rays, MRI, and sometimes ultrasounds. Injections can be used to both treat the pain and to identify the location of the pain. The abnormal bony shape causing FAI can usually be identified on plain x-rays, although sometimes a CT scan is performed to help see the deformity in 3 dimensions. The MRI can help identify tears to the labrum and damage to the cartilage.

Femoroacetabular Impingement,Hip Impingement,Cam Impingement
MRI showing cam impingement and a tear of the labrum. Credit: Gallo RA, Silvis ML, Stuck D, Mosher TJ, Lynch S, Black KP. Hip Labral Tears Among Asymptomatic Hockey Players Identified on MRI: Two-year Follow-up Study. Poster presentation, American Orthopaedic Society for Sports Medicine, Annual Meeting, Chicago, Illinois, July 10-13, 2013

Treatment Options for FAI

There are some great treatment options for FAI. In some cases, nonsurgical methods such as physical therapy or injections are helpful. Often times, avoidance is helpful. This means learning which sitting and functional positions put cause more impingement in the hip, and avoiding these positions.

In other cases, surgery is performed. Most the time, surgery is performed arthroscopically using 2-3 small incisions. An arthroscope (small camera made for the joint) is used to visualize the hip and assist in repairs. If there are labral tears, they are usually repaired back to the bone. The extra bone causing the impingement (either the cam or pincer lesion) is resected back to a more normal shape. Other conditions can be treated during the surgery including snapping of the psoas tendon.

Frequently Asked Questions About Hip Impingement

How do you fix femoroacetabular impingement?

Surgical treatment for FAI involves arthroscopic surgery that trims back some of the excess bone from the cam lesion and repairs any labral and cartilage damage.

Does femoroacetabular impingement go away?

Without surgical treatment, the x-ray findings will not change. However, it is possible for the pain to go away with non-surgical management. This usually consist of avoidance, rest, rehabilitation, and sometimes injections.

What does a hip impingement feel like?

Hip impingement usually results in pain in the groin area, made worse by certain activities like sitting and bringing your knee to your chest.

What is femoroacetabular impingement caused by?

FAI is caused by excess bone that restricts the normal motion of the hip.

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