Femoral Acetabular Impingement (FAI)

Femoroacetabular Impingement (FAI)

A femoroacetabular impingement or FAI is a medical term that refers to a wound resulting from hip bones that do not snugly fit together and cause friction at the contact points which eventually results in long-term damage to the joint. Specifically, the top of the largest leg bone (femora) is restricted in some way from rotating and moving around normally and this causes a wound to the hip bone socket, known by its medical term as the acetabular socket.

How Femoroacetabular Impingement Injuries Occur

FAI is somewhat unique among hip wounds because few symptoms present themselves at the initial stage of the damage and are only usually made known after several years. Many people only begin to realize that they may have FAI when their hip or groin starts to feel stiff, achy, and inflexible.

Over time, the friction involved with rotating and moving around the femur bone and its hip bone socket starts to wound the soft cartilage on the top of the leg bone. Other damage sustained by an FAI injury is when the cartilage inside the socket itself becomes worn down and inflamed. Advanced cases of FAI are considered a form of arthritis in the hip area.

Who Is Vulnerable to a Femoroacetabular Impingement Injury

While anyone with an improperly fitting femur and hip bone socket can eventually develop FAI, the condition is more prevalent amongst career sports players due to the years of strain and pressure they put on rotating and moving the hip joint that connects to the biggest leg bone.

Doctors believe that anyone can develop an FAI injury if the top of their large leg bone and/or hip socket is misshapen in some way. Uniquely, men tend to develop a category of FAI injuries known as a “Cam” wound in which the top of the femoral bone is too large and thus grinds against the hip bone socket. Women tend to develop the “Pincer” form of FAI wounds, caused by too much tissue on the hip bone socket. Overall, most FAI injuries involve both the “Cam” and “Pincer” form of the ailment.

FAI wounds are more prevalent among people who spend a lot of time on their feet. A number of vigorous activities, including golf, hockey, lacrosse, martial arts, tennis, baseball, volleyball, soccer, and rowing can make the condition worse but only if an underlying malformation of either the femur bone or hip bone socket already exists.

Symptoms of a Femoroacetabular Impingement Injury

Because the wound takes years to make itself known, many individuals with an FAI injury have no noticeable symptoms. Once the ailment has begun to get worse, individuals may realize they’re feeling a number of symptoms, including:

  • Discomfort experienced in the side of the hips.
  • Tightness or lack of flexibility in the front of the hip.
  • A marked increase of hips feeling tight after periods of not moving around or following a round of vigorous exercise.
  • A dull, aching discomfort experienced in the butt, pelvis, or lower back.
  • Sharp, intense discomfort when squatting, dancing, turning, jumping, or twisting.

Treating a Femoroacetabular Impingement Injury

Most cases of FAI must be diagnosed by a doctor and are identified by performing special range of motion scans to determine the source of the discomfort experienced in and around the hip. In some cases, an X-ray, CT or MRI scan may be used to identify degradation to the cartilage on top of the femur and inside the hip bone socket.

For people who are not professional sports players, the standard course of treatment of an FAI injury is to take it easy, avoid vigorous physical activity, and perform strengthening and mobility movements. To minimize any tenderness or physical discomfort, taking small amounts of OTC drugs can also be helpful.

For professional sporting types and individuals with more severe cases of FAI, surgical intervention may be required. Arthroscopic surgery is the most common method of fixing damage to the cartilage and removing excess material or reshaping the top of the femur and/or hip joint socket.


In this instance, an athlete was originally diagnosed with minor quadriceps muscle strain and was treated for four weeks, with unsatisfactory results. When he came to our clinic, the muscle was not healing, and the patients’ muscle tissue had already begun to atrophy.

Upon examination using MSUS, we discovered that he had a full muscle thickness tear that had been overlooked by his previous provider. To mitigate damage and promote healing, surgery should have been performed immediately after the injury occurred. Because of misdiagnosis and inappropriate treatment, the patient now has permanent damage that cannot be corrected.

The most important advantage of Ultrasound over MRI imaging is its ability to zero in on the symptomatic region and obtain imaging, with active participation and feedback from the patient. Using dynamic MSUS, we can see what happens when patients contract their muscles, something that cannot be done with MRI. From a diagnostic perspective, this interaction is invaluable.

Dynamic ultrasonography examination demonstrating
the full thickness tear and already occurring muscle atrophy
due to misdiagnosis and not referring the patient
to proper diagnostic workup

Demonstration of how very small muscle defect is made and revealed
to be a complete tear with muscle contraction
under diagnostic sonography (not possible with MRI)


Complete tear of rectus femoris
with large hematoma (blood)


Separation of muscle ends due to tear elicited
on dynamic sonography examination

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