Updated: May 5, 2022
Femoroacetabular Impingement (FAI) is a condition that is thought to be present in 30% of people according to a study by Wall, et al. It refers to an impingement of the hip joint. The hip joint is a ball-in-socket joint with the head of the femur being equivalent to a ball inside the socket of the acetabulum. Another important structure is the labrum, which provides extra support to the acetabulum and more stability for the femur. The labrum is not bone, rather it is made up of cartilage. The hip joint is deeper and a more secure socket than the shoulder joint, which is why we have less hip range of motion compared to the shoulder.
The hip does require significant mobility in multiple directions, which requires the femur to glide smoothly in the acetabulum. Unfortunately, there can be cases where either the acetabulum or the femur have bony overgrowths as shown in the image below
The first image shows a normal hip with the femur and acetabulum remaining congruent and some support from the labrum. The second image demonstrates a cam impingement, which occurs when there is bony growth on the femur. The third image is a pincer impingement, which is when the bone grows on the acetabulum. Both are not ideal because if you imagine the femur rolling in the acetabulum, it will run into the bony overgrowth which prevents movement.
Not only can the cam and pincer impingements limit movement, but they can create multiple issues including damage to the labrum. As I mentioned before, the labrum is made of cartilage that can be worn away. This can lead to less support for the femur along with labral damage creating more impingements. Sometimes the damaged portion of the labrum can float and create more barriers to movement along with pain.
There are two possible causes of FAI: genetic and acquired. Genetic factors can include the presence of extra bone growth from birth or an enlarged femoral head that creates stress and causes the bone to grow abnormally. It is important to remember that your body will create more bone in areas of stress. This is helpful when we are growing and want to create stronger bones, but it can lead to bone in inappropriate places if there are uneven forces. It is also thought that activities when you are younger can develop FAI particularly if you are involved in repetitive stressful hip movements during sports.
Interestingly, there are gender differences in FAI presentations. A study by Raveendran, et al. showed that 1 in 4 men have a cam deformity while only 1 in 10 women will have it. Interestingly, 1 in 15 men and 1 in 10 women have a pincer deformity. It is not known why these numbers are skewed, but it does show the relationship between our growth and development with the presence of FAI.
Femoroacetabular Impingement Symptoms
Symptoms of FAI can be divided into two categories: pain and tightness. Pain is usually the cause of someone seeking treatment and can range from annoying to debilitating. Pain is normally felt in the groin or front of the hip. Rarely it can be in the back of the hip, but the front and inside of the hip are much more common. The pain is normally worse with deep hip flexion such as when squatting, sitting, or climbing some stairs. It can also be worse with prolonged positioning such as sitting for hours at a desk with a low chair. Oftentimes weightlifters will notice they are not able to get into as deep of a squat without pain.
In cases of pain, usually the deformity is compressing nerves or sensitive tissue. In situations where tightness is the primary complaint, the excess bone may be creating a stopping point for movement. This can manifest in locking, clicking, or catching sensations while moving the hip. Muscle tensing and spasming in the area may be part of the reason for mobility limitations, but the bony overgrowth is the root cause.
Femoroacetabular Impingement Diagnosis
Diagnosing FAI can be difficult due to the genetic component of the deformity. Many people have cam or pincer deformities and do not realize it. Therefore, imaging that reveals an overgrowth could be a false positive due to the patient having that deformity their entire life and it not playing a role in their current episode.
A consensus paper by hip experts Griffin, et al. found that there are three criteria that should be met in order to diagnose FAI. The first is that the patient’s complaints should line up with typical symptoms as discussed above. The second should be a clinical examination which usually includes the FADIR test as shown below courtesy of orthobullets.com
This test is attempting to impinge the hip by flexing it and internally rotating to compress the deformity. The test is shown to be highly sensitive but with poor specificity. Tests that show these characteristics tend to be positive for a lot of people. Therefore, if the test is negative then it is relatively certain that the person does not have FAI. However, this position is uncomfortable and possibly painful for many people who do not have FAI.
The final component of FAI diagnosis is imaging, X-rays are typically sufficient to see bony growth, but MRIs are sometimes needed to examine the soft tissue including the labrum. If there is minimal soft tissue damage, then the problem may not be the deformity, even if one is present. It is important to consider all three qualifications in diagnosing FAI.
Pictured above is a cam deformity. You can see there is a small bony overgrowth on the head of the femur that will run into the rim of the acetabulum. These deformities can appear to be very small and still cause significant symptoms.
Femoroacetabular Impingement Treatment
Treatment for FAI is complicated because there are not many options available and they all have similar success rates. Because of this, most healthcare providers will start with physical therapy and possible nonsteroidal anti-inflammatory drugs (NSAIDS) which include ibuprofen. It can take several months to see improvements in some FAI cases, so it is important to continue conservative treatment as long as possible.
If a provider wants to use a more targeted approach, corticosteroid injections into the hip joint can decrease swelling significantly. An injection is more precise, but it subjects the tissue to high doses of steroids, which can lead to degeneration of the cartilage. The goal of an injection is to provide more mobility for physical therapy to progress and it may be a beneficial adjunct therapy if determined by you and your provider.
The final option involves surgical resection or repair. Typically, a surgeon will perform minimally invasive surgery and trim the part of the bone that is overgrown along with any damaged tissue. If there is a significant labral tear, then they may need to repair it and sew it into place which delays recovery. Surgery is typically a last resort as it results in increased recovery time and a slow progression to full movement. It is also important to address any deficiencies after surgery so that the deformity does not reform.
Femoroacetabular Impingement Physical Therapy
Physical therapy for FAI can vary significantly depending on the symptoms. Most people benefit from some manual therapy including trigger point dry needling to decrease muscular guarding of the area. Relaxation of the muscles can lead to smoother movement in exercises immediately following manual therapy which can provide long term benefit.
It is important to look for root causes of FAI and decreased mobility in other regions of the body can be a cause. Poor lower back mobility can increase force on the hip. Pelvic mobility can also be a key component that is often overlooked. Moving better at other points in the body can provide huge benefits while waiting for the hip to heal.
Workload is also strongly associated with FAI symptoms. If you have pain when playing soccer and you play 6 days a week, you will probably need relative rest to allow for healing. Complete rest may be required depending on the se