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What is FAI (Femoroacetabular Impingement)?

Femoroacetabular impingment (known as FAI) is a condition that has recently attracted a lot of attention in the orthopedic community. It is a condition where abnormal hip architecture leads to pain and pre-mature arthritis of the hip.

A basic understanding of our hip anatomy is critical to understanding this condition.  Our hip is a joint where two bones come together: the thigh bone (aka the femur bone) and the pelvis bone (aka the acetabulum).  As you can see the name FAI is derived from combining these two bones.  The term "Impingment" refers to the fact that one bone is inappropriately bumping into the other.  There are two types of impingement;

1) Cam impingement: the femur is abnormally shaped (it has a short thick neck).  This is classically associated with young athletic males (although new research suggests that this type of impingement is most common in men and women of all ages).  

2) Pincer impingement: the acetabulum is abnormally shaped (its angled back too far "retroverted" and overhangs). This type of impingment is commonly associated with middle-aged women.

FAI is a hot topic because many orthopedic surgeons believe this condition may explain why some people develop severe hip arthritis that eventually requires a hip replacement (see talk).  One of the biggest questions remaining in orthopedics is why some people get arthritis and not others (because the majority of people don’t have rheumatoid arthritis or other autoimmune inflammatory condition and are in otherwise good health).

Diagnosis of FAI:

People with FAI report groin pain and hip pain, and particular problems with sitting (because its most painful when flexing and internally rotating the hip).  Usually the pain occurs daily, and there is no history of a traumatic injury. Interestingly women tend to report more pain, stiffness, and problems with daily activity (even when the impingement doesn't look as bad on x-rays).

The first tests ordered for diagnosis is an x-ray of the hip and pelvis to look at for abnormal architecture of the bones, and to rule out other causes of hip pain (like arthritis or a broken bone).

There are different patterns which can specifically suggest FAI. An MRI can also be useful to evaluation the hip for sites of damage, particularly the soft tissue (like cartilage and the labrum which are located inside of the hip joint) as well as bruising to the bone (seen as "edema", aka swelling, within the bone).

Treatment of FAI: 

The condition is treated based on the severity of symptoms and the x-ray findings. 

If someone has only minimal symptoms of pain or disability then nonsurgical management is ideal. Physical therapy and anti-inflammatories are often effective at treat the problem.

If the pain is more significant, and nonsurgical treatment has failed to provide relief, then there are surgical procedures to correct (or improve) the underlying abnormal architecture of the hip. The classic surgical treatment for FAI is to make an incision over the hip, dislocate the hip joint, and then shave down the abnormal bump causing pain.  If this sounds to you like a big procedure, you are correct, its no joke.  But it has been shown to provide many people with relief.  

However, advances in surgery have shown than many cases of FAI can be treated less invasively, using a small camera and tools via Arthroscopic Surgery.  In this case, a few small skin incisions are made, the hip is never dislocated, and most cases the same results can be achieved.    

If the disorder doesn’t get recognized until older age when significant arthritis has already occurred, a hip replacement is probably the ideal solution, because its too late to fix the underlying problem (as some say: the horse has already left the barn years ago).

What are the long term outcomes:

FAI is a topic that is starting to gain more attention in the field of orthopedics and therefore there is not a lot of information about long term outcomes.  There have been studies looking at short term and long term outcomes after surgical treatment (either with the larger hip dislocation procedure, or with the arthroscopic treatment).

All types of surgery appear to improve pain in the majority of people.  Remember that the other goal of surgery is to restore normal hip architecture to prevent early-onset arthritis.  The effectiveness of surgery in preventing hip replacements in people with FAI appears to depend on how early the condition is identified and treated.  If FAI is caught early, and there is no signs of arthritis, then it seems to help.  However one study (Beck et al) looking at 19 people undergoing FAI surgery showed that 25% still needed a hip replacement within just 5 years.



1) Ganz R et al. Femoroacetabular impingement: a cause for osteoarthritis of the hip. CORR 2003; 417: 112-20. full article.

2)  Nepple JJ et al.  Clinical Presentation and Disease Characteristics of Femoraoacetabular Impingement Are Sex-Dependent. JBJS 2014; 96: 1683-9. full article.

3) Philippon MJ et al.  Outcomes 2 to 5 years following hip arthroscopy for femoroacetabular impingement in the patient aged 11 to 16 years. Arthroscopy 2012; 28(9): 1255-61. full article.

4) Parvizi J, Leunig M, Gaz R. Femoroacetabular impingement. JAAOS. 2007; 15(9): 561-70. full article.

5) Simpson TG. Arthroscopic treatment of femoroacetabular impingement. Am J Ortho. 2008; 37: 608-12. full article.

6) Beck et al. Anterior femoroacetabular impingement: II. Clinical midterm results. CORR 2004. 418: 67-72. full article

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