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Cam and Pincer impingement anatomy of the hip.

FAI: All About Femoral Acetabulum Impingement

Femoral acetabulum impingement (FAI) is a condition where the front of the thigh bone (femur) and the bone of the hip joint (acetabulum) contact too early, causing pain, usually in the front of the hip or groin.

FAI is also known as hip impingement. This term reflects the same idea that the hip joint is being impinged upon, or pinched, due to abnormal bone shape or contact between the thigh bone (femur) and the hip joint bone (acetabulum). Additionally, FAI is also known as Cam impingement and Pincer impingement.


Examples of FAI also known as hip impingements.


In this blog, we’ll cover the causes, symptoms, and diagnosis of FAI. And weigh in on surgery vs movement as an intervention.


The two causes of FAI

The first cause of FAI is when the femoral head angle is larger than normal (although there isn’t a clear definition of what ‘normal’ is) and prematurely contacts the acetabulum causing the impingement.

The second cause for FAI is a larger than ‘normal’ lateral side of the acetabulum. Again, the femoral head contact with the acetabulum earlier than normal, causing the impingement.

The larger femur head variation of FAI tends to be more prevalent in men. Whereas women have a higher chance of suffering from FAI with the laterally extended acetabulum.

That being said, it is possible to have an FAI that’s simultaneously caused by both the larger femoral head and the larger lateral acetabulum.

Symptoms of FAI

The most common symptoms associated with FAI are a pain in the hip or groin, but sometimes also in the back, butt, or thigh.

There might also be clicking, stiffness or limited range of motion, especially in the end ranges of movement. Such as at the bottom of the squat or movements like sitting or standing up from a chair.

The symptoms of FAI (Femoroacetabular Impingement) can include pain in the hip and groin area, stiffness, and difficulty with certain movements such as sitting or standing up from a chair. Some people may also experience a clicking or popping sensation in the hip. In some cases, the symptoms may be similar to those of other conditions such as hip arthritis or a labral tear, so a proper diagnosis is important.

Diagnosis of FAI

The quickest way to diagnose FAI is the FADIR test, where the practitioner brings the hip into flexion, adduction, and internal rotation. If you’ve got no symptoms in this position, it is likely that you do not have FAI.

Try Our Express Hip Assessment

Our hip assessment is done in 8 minutes and will help tell you if you have any hip impingement.

If there’s pain, you’ll still need imaging to confirm the FAI diagnosis. It’s worth noting that, in most cases, you don’t need imaging to begin rehab. As the imaging rarely changes what you’d do in rehab anyway.

Imaging on its own isn’t enough

It is possible to have changes in the femur or acetabulum without experiencing any symptoms. A systematic review in 2016 concluded that these changes are present in 22% of individuals with zero symptoms of FAI.

The bottom line? Pain is your first guide. Not the image.

Surgery and FAI

Surgery is usually the last resort due to the associated risks, uncertain benefits, and higher costs. A systematic review in 2020 found that there was only a small positive benefit of having surgery compared to physical therapy at 8-12 months, but no significant difference at 2 years. 

Another research in 2018 concluded that, after surgery, 60-70% of patients get better, 50% of patients feel good, and 20-30% return to normal function.

Further, a 2019 study found that conditions such as mental health issues, chronic pain, cardiometabolic problems, and sleep disorders all significantly increased after FAI surgeries.

Unfortunately, it seems that FAI surgeries are following a similar trend to that of shoulder “impingement” surgeries. Both are overprescribed and often seen as the first option. When neither one should even be in the discussion until all the other avenues of intervention are exhausted.

Whether the overprescription of surgeries is a symptom of our overspecialized medical system, or something else, is a debate for another time.

Movement should be your first intervention for any hip impingement


Improving strength, managing your load, and temporarily modifying your activities are three of the most important aspects of FAI rehabilitation. A good rule of thumb is to stick with the movement-based approach for at least 3-6 months before considering surgery.

We’ve got a great hip mobility program that will give you 12 weeks of structured programming.

We also recommend connecting with a knowledgeable movement practitioner who is up to date with the evidence-based approach to FAI treatment. You can schedule a consultattion directly with Ian. 


In the rare case that you do need surgery, all that strength work you’ve put in will improve your surgery recovery. And likely speed up your return to the activities you love.


Next up: Our recommend exercises to help with FAI and hip impingement.




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