Femoral Acetabular Impingement (FAI)

Femoroacetabular impingement

Regardless of your age, hip pain can be debilitating. The hip joint is one of the most complex joints in the body. It is also critical to your ability to be mobile. In other words, to get around successfully.

There are many different things that can cause hip pain. The potential causes include strains, osteoarthritis, referred pain from other joints, inflamed bursa and femoroacetabular impingement (FAI). Any of these can require professional treatment. Conservative treatment would start with noninvasive approaches, such as physical therapy.

That last condition is the one we will focus on here and it is a big word, so let’s start by breaking it down and explaining what the means. The hip is a ball-and-socket joint. Femur is the medical word for the thigh bone. The top of the thigh bone is rounded. It is called the head of the bone. It serves as the ball part of this joint. Acetabulum is just the medical word for the part of the pelvis that forms the socket. So, you get the big fancy word “femoroacetabular” by putting the words “femur” and “acetabulum” together. Outside of the medical profession, most people would just say “hip.” The femur plus the acetabulum make up the hip joint. Impingement just means that something is interfering with the normal range of motion for the joint in question. It is not moving the way it normally would. It is being limited in some manner.

Methods for Searching and Selecting Data

We have already talked about the bones involved — the femur and the acetabulum. However, a functioning joint in a living person involves more than just the two bones that meet in that area. There are also tendons, ligaments, cartilage, and muscles involved. All of those different kinds of tissues are necessary to make the joint work at all. They each have a different function in making it work, in making it move the way it does.

The tendons and ligaments basically serve as anchors for the muscles and other structures. You can think of them as similar to the thread that holds your clothing together. They connect things. This is an important function, essential to the ability of the body to move. They are connected in a way that allows for freedom of movement, creating a certain amount of tension that holds things together, but not so much as to prevent motion. It is a kind of balancing act, so to speak.

Cartilage provides essential cushioning so that the bones do not rub together too hard. When the cartilage is damaged, the joint get painful because it lacks the cushioning it is supposed to have. In the hip, this cushion is called the labrum. It is a circular bit of cartilage covering the acetabulum. In addition to provide cushioning, it also helps the head of the femur fit snugly in place. This is critical to the functioning of the joint. You need some freedom of movement to function at all, but not so much that the hip becomes easily dislocated.

The muscles provide the motion. Because of the unusually complex range of motion of this joint, there are many muscles that get involved in making it work. Flexor and extensor muscles allow it to bend together and then unbend. The abductors and adductors allow motion towards the midline and away from the midline. In essence, one set of these muscles — the adductors — allows you to move your legs apart and the other set — the abductors — allows the legs to move towards each other.

There are also hip rotator muscles that allow for circular motion unique to ball and socket joints. You see something similar in the shoulder. Most joints in the body cannot do this. Most of the joints of the human body only bend and unbend. The hip is fairly unique in having a complex range of motion.

Two Basic Types of Impingement

There are two important different categories of femoroacetabular impingement. The first kind is a pincer defect. This is a situation where there are bony growths on the acetabulum. This is seen in women more often than in men.

The second category is called a cam defect. This is a kind of slang and is short for camshaft. In this case, the excess bony growth is on the head of the femur. It is frequently seen in relatively young men. Unsurprisingly, this is frequently a sports-related issue.

One medical study of the causes of FAI involved 44 patients. Half of them were known to have FAI and half were control subjects with similar age, weight and other particulars. The conclusion of the study was that FAI not only causes hip pain, it also leads to early onset osteoarthritis. Damage from sports activities can wear away at the cartilage and cause FAI. This leads to impairment of the function of the hip joint, as well as pain and discomfort, sometimes at relatively young ages.

Other studies have suggested that FAI is present in approximately 15 percent of people with no symptoms at all. Unsurprisingly, FAI is found to be present in far more patients who do have symptoms. It is present 80 percent of the time when there are symptoms, such as hip pain and clicking of the hip when in motion. A study of more than 3000 individuals confirmed that cam deformities are more common in men and pincer deformities are more common in women. Athletic injuries or stress injuries are the common cause for younger patients suffering from this condition. In the elderly, it is more often due to arthritis.

When Patients have Hip Pain

Some of the issues seen in patients suffering from FAI include groin pain, knee pain, ankle pain and general leg pain. The problem in the hip can throw things out of alignment such that other muscles, joints, tendons and ligaments are stressed. Everything in the body is interconnected. If the hip has a serious problem, all joints, muscles and other tissues involved in ambulation will be impacted to some degree. For some people, this means that one of the most obvious symptoms of a hip disorder is not hip pain but pain in one of the related joints.

Additionally, FAI limits motion of the hip. It can limit moderately or substantially. Depending upon the daily activities of the patient in question, this may or may not be obvious. Athletes may be far more aware of the limited range of motion than nonathletes, but that doesn’t mean a nonathlete is not impaired or limited by it.

Many people with FAI are between 20 and 40 years of age. In most cases, their pain and decreased range of motion can be traced back to their involvement in sports or exercise. In contrast, people with osteoarthritis not related to FAI are typically over the age of 50. If they have an injury, such a labral tear, it is frequently due to a fall rather than due to involvement in athletics. For elderly people, falls in the bathroom are common and can cause serious injury. Even so, in some cases, they can be returned to a full range of motion with appropriate treatment, starting with physical therapy. Physical therapy is the first thing that should be tried because it is noninvasive and has minimal side effects. Drugs and surgery should only be sought out when other therapies have failed to provide adequate relief and healing of the issue.

Some of the things which a physical therapist will work on include strengthening of specific muscles that have been medically determined to be insufficient to the load they should be carrying and joint mobilization. In other words, physical therapy very often starts with the basics of trying to make the patient both stronger and more limber so that the range of motion of the joint is not limited. In many cases, physical therapy alone can achieve the stated therapeutic goals of the patient in question, such as a desire to resume walking 2 miles a day or a desire to ride horses. In many cases, after physical therapy has been concluded, such activities can be pursued without limitations and the patient can resume a full and active life.

Other options include low dose ultrasound, arthroscopy and arthroplasty. In cases where full recovery is not possible, recommendations can be made for how to modify activities appropriately so that they can be pursued safely and without pain. Some patients have to repeat physical therapy or try several different approaches to treatment before the issue is worked out as best it can be. However, ongoing hip pain and moderate limitations on the range of motion may persist. The therapeutic goal is not just about personal comfort. Reducing or eliminating hip pain can improve the quality of life, but a more important goal involves functionality. Whether you have some hip pain or not, can you still go about your life and do the things you need to do?

Getting a Diagnosis

If someone has symptoms and suspects impingement of the hip joint, the first thing that needs to happen is a physical examination by a qualified medical professional. They will use a few different techniques to assess the degree to which him motion is limited, if at all. They will write down any symptoms reported to them verbally. They will also check the posture against a plumb line to determine how out of alignment the joints are and which muscles groups and tendons may be involved.

They may ask you sit in odd positions in a chair or stand in odd positions while they observe. They may measure the length of both legs. The legs should be the same length. A significant difference in leg length can suggest the tendons and ligaments of one leg have been shortened and the body is out of alignment. This can often be corrected with appropriate therapies. A difference in length can be an important clue to the causes of your hip pain and other related pain, such as referred pain involving one or both of the knees.

If a physical exam alone is not satisfactory for drawing a conclusion, an MRI may be ordered. This can detect any bony prominence which may be present in the hip joint. Bony prominences are the crux of the issue with FAI. As noted above, they can occur on either the acetabulum or the head of the femur. On the acetabulum, they are called a pincer defect and on the femur they are called a cam defect. In either case, they are known to interfere with hip motion and cause loss of internal rotation, as well as hip pain.


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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