Femoroacetabular impingement (hip impingement)

Femoroacetabular impingement (hip impingement)

Learn more about the Young Adult Hip Preservation Program

What is femoroacetabular impingement?

Femoroacetabular impingement (FAI), also called hip impingement, is a condition where the top of the thigh bone (femoral head) does not fit properly into the hip socket (acetabulum). This mismatch can lead to abnormal contact between the “ball" and the "socket” of the hip joint when the hip is being bent (in flexion).

Over time, this repetitive motion of the abnormally shaped hip joint can cause pain and limit hip movement. It can also damage the labrum, the O-ring type soft tissue structure that runs along the rim of the hip socket. In severe cases, there can be damage to the articular cartilage that lines the socket as well.

FAI is more common in males than females, and often affects active individuals involved in sports that require a lot of hip bending (flexion), running and rapidly changing directions. 

  • Kathleen J. Maguire, MD: Femoroacetabular impingement, which we call FAI for short, is a condition where there is mismatch in the shape of the hip joint. There's some abnormality between the socket and the ball so that when patients bring their hip into flexion, they're making premature contact, which can result in pain, it can result in limitations in terms of motion. With everyday activities, patients can experience clicking or popping in the front of the joint. Patients often will come in with what we call the C sign. They say they can't quite pinpoint it exactly, but they'll cup their hand in a C shape around their hip and say it kind of hurts right there. And having hip pain, I often describe it's like having a really bad toothache. Every single motion that we do, again, up and down stairs, sitting at school, being able to drive, it can really be a challenge just with everyday life. Wudbhav N. Sankar, MD: The pain can typically start low grade, maybe just a little bit with activity, but if it gets worse, and it can start bleeding into normal life and creating pain with even upright activities like walking and climbing stairs. Kathleen J. Maguire, MD: So some people, unfortunately, are more prone to developing hip impingement. We know that males are more commonly affected than females. We also know that patients who are athletes or involved in particular sports are more likely to develop hip impingement. Wudbhav N. Sankar, MD: It's a 60 to prone internal. 30 of pro external FAI really is a diagnosis that has to be made by putting together all of the information. You need to have a good physical exam to see how the hip moves, how a person's walking, what their range of motion is like. You have to get nice quality X-rays to get good understanding of how the hip looks in three dimensions. Sometimes we need advanced imaging studies like CAT scans or MRIs as well to make the diagnosis, and one of the key parts of making the diagnosis is actually getting a good history. Understanding how the patient is feeling, what type of pain they have, what kind of activities are painful, and what positions are most problematic. And that's really key for making an accurate diagnosis. Kathleen J. Maguire, MD: A lot of patients will come to me with hip pain and groin pain and hip impingement and this really can affect not only their ability to participate in sport, but just their ability to get through the day without discomfort. And getting those kids back to their tip top playing shape and getting them back on the field is a really big part of what I do. So typically when a patient presents to us with FAI we do start with non operative management. That means that we talk about activity modification, prescriptions for medication, sometimes really strong anti inflammatories that can help to kind of relax agitated or inflamed muscles around the hip. And we get patients into a physical therapy program to really provide a specific protocol that's just for kids who present with FAI. In addition to doing physical therapy, we also provide ultrasound guided injections. We're able to place a medication that helps not only with pain, but also inflammation inside the joint itself or in the surrounding musculature of the hip. So the injection really provides, we say, a window of opportunity to maximize physical therapy, to build strength, stability of the pelvis and the hip to hopefully prevent need for a surgery. We start to talk about surgery for patients who have failed non operative interventions. Hip arthroscopy is a minimally invasive way to manage a number of conditions inside the hip. I think it offers a lot of benefit because it is minimally invasive. It's done through small portal sites. We don't have to make large incisions. We don't have to dissect through a large amount of musculature. I tell a lot of the kids, it's like playing a video game. You're kind of watching what's going on inside the hip up on a screen, and then we're able to do all of our work kind of outside the body. So a lot of patients can forego a larger surgery, which unfortunately can mean a longer recovery, by having hip arthroscopy done. Wudbhav N. Sankar, MD: So in certain circumstances, hip arthroscopy is not going to be enough. So in situations where the socket is abnormally rotated, over the front, then the best thing to do is actually periacetabular osteotomy, which is an operation that detaches the hip socket and reorients it into a better position. Similarly, if there are rotational problems on the femur bone, then sometimes we have to do what's called a derotation osteotomy, and that's a procedure where the femur bone is actually cut, rotated it into a better position and then fixed with either a rod or a plate. Now some of these procedures seem and sound pretty drastic, but there are certain situations where it is the better treatment option, so they can get back to the field and back to their activities as soon as possible. It's important to see a pediatric orthopedist who has a specialty in femoroacetabular impingement. Kids have unique skeletons that are growing, and any kind of treatment really needs to focus on the unique aspects of the pediatric skeleton. Kathleen J. Maguire, MD: I really impress upon the kids that surgery is the first step to recovery, it's certainly not the last. So after surgery, most of our patients will undergo a long post operative course of physical therapy, that really is to get their strength back, getting them going up and down stairs, working on their agility, their flexibility. All those types of things that hopefully will help not only get them back on the field, but help prevent another injury in the future. Wudbhav N. Sankar, MD: After treatment for FAI, our expectation, and certainly the expectation of our patients, is that they get back to an active lifestyle. Kathleen J. Maguire, MD: A lot of our athletes are very active now, and they want to continue to be active. Keeping them out of pain and keeping them as functional as they want to be is really, really important to me. It's why I do what I do Wudbhav N. Sankar, MD: When they have that smile on their face and they come back for their post operative appointment and they've been able to do what they haven't been able to do for several months or years, that's when I just go home with a great feeling. That's exactly why I wake up in the morning and come to work.
Transcript Transcript

Symptoms of hip impingement

Some people with FAI can live active lives and never experience pain or hip problems. Others – especially athletic and active people – may feel pain in their hip or thigh. This pain is often worse when sitting down or standing for a long period of time. Individuals with FAI may feel a clicking, popping or a pinching sensation deep inside their hip joint. Sometimes the hip can lock up or feel like it gets stuck in certain positions.

Pain due to FAI typically begins as mild with activity, but often worsens over time and may cause pain with upright activities such as walking and climbing stairs. 

Types of hip impingement

There are three types of hip impingement: 

Pincer impingement, where the hip socket (acetabulum) is misshapen, too deep, or extends further over the "ball" (top of the thigh bone) than normal.

Pincer external view

CAM impingement, where there can be a prominent bump on the top of the thigh bone (femoral head), or "ball," causing it to be fuller or flatter than normal.

cam cross section

Combined pincer and CAM impingement, where both sides of the hip joint (both the ball and socket) are misshapen. 

CAM Pincer exterior

Diagnosis of hip impingement 

A diagnosis of FAI may be suspected after a clinician has gotten a detailed patient history and performed a physical examination. During the exam, the doctor will evaluate how the patient’s hip moves while walking, standing and sitting.  

Clinicians may ask patients to: 

  • Describe the type of pain they feel,
  • Explain what type of activities cause pain, and
  • Explain which positions are most problematic. 

X-rays can help clinicians evaluate the shape of the ball (top of thigh bone) and hip socket to look for possible causes of impingement. X-ray findings can be subtle. It’s important to seek pediatric orthopedic experts who can accurately diagnose the condition and determine next steps.  

Children’s Hospital of Philadelphia (CHOP) offers advanced imaging to help doctors see and understand what’s going on deep inside the patient’s hip socket. We may recommend added specialized imaging studies – all of which are available at CHOP – including:  

  • 3-D reformatting imaging, which uses a combination of X-rays and computed tomography (CT) scans to create three-dimensional models of the hip anatomy.
  • Delayed gadolinium-enhanced MRI of cartilage (dGEMRIC), an imaging technique that focuses on finding early cartilage breakdown. This method helps map areas of early osteoarthritis or specific cartilage injuries.
  • Radial hip plane imaging, which uses MRI to take image slices of the hip joint around the ball and socket. This method helps find areas of possible FAI impingement better than traditional X-rays.  

Treatment for FAI/hip impingement

Treatment for hip impingement typically starts with non-surgical options such as activity modification, physical therapy, ultrasound-guided injections and/or anti-inflammatory medications. Medications – whether by mouth or injection – offer patients relief from pain while they receive physical therapy support. The goal is to build strength, endurance and stability in their pelvis and hip in the hopes they can avoid the need for surgery.

If patients do not improve with non-surgical treatment, hip arthroscopy – a minimally invasive surgery – may be recommended. In hip arthroscopy, surgeons make a few small incisions on the outside of the hip, then use special tools to reshape how the thigh bone and hip socket fit together. Additionally, for patients with a torn hip labrum, the arthroscopic surgeon can clean and repair the labrum with stitches via a minimally invasive procedure.

For many patients, hip arthroscopy relieves pain from FAI and improves the function of the hip joint so they can continue their lives. 

 In some cases, hip arthroscopy is not going to be enough. Instead, a larger, more complex surgery may be the best option. Hip specialists can help determine which surgery will be best for each individual patient based on their history and workup.

Surgical procedures used to correct hip impingement include:  

  • A periacetabular osteotomy (PAO) changes the orientation of the hip socket. In this procedure, part of the pelvis is cut and repositioned, so the hip socket and ball of the thigh bone are better aligned.
  • A derotational osteotomy corrects a deformity in the thigh bone. In this procedure the femur is cut, rotated into a better position, and then secured with a rod or plate.  

What to expect after surgery

After surgery for FAI, it will take time for patients to regain their strength. Patients will need physical therapy to regain skills needed for everyday life like going up and down stairs and getting in and out of the car. Patients will be taught exercises to increase strength, agility and flexibility.  

The goal of physical therapy after surgery is to help patients resume an active lifestyle – whether that includes playing a sport or not – and to prevent another injury in the future.

Long-term outlook 

After treatment for FAI, patients are encouraged to follow-up annually with CHOP’s Young Adult Hip Preservation Program – even into their 20s and 30s. In most cases, patients resume active lives, playing sports, raising families and enjoying many other activities.  

Why chose CHOP for FAI treatment?

Orthopedic surgeons and physicians at Children’s Hospital of Philadelphia (CHOP) provide expert care, cutting-edge treatments and the best outcomes for all types of hip disorders that began with or developed in childhood. Our Young Adult Hip Preservation Program is part of the nation’s #1 ranked pediatric orthopedic program in the world according to U.S. News & World Report’s 2024-2025 rankings of the nation’s top children’s hospitals. 

For some, a hip disorder doesn’t become problematic or painful until adulthood – but often stems from an underlying pediatric hip condition. The causes and treatment for disorders like femoroacetabular impingement require the expertise and knowledge of doctors – like those at CHOP – who understand the full developmental spectrum of the human hip. Unlike adult providers who may suggest a hip replacement, CHOP physicians aim to reconstruct and enhance the natural hip and hip socket to prolong the function of the natural hip – decreasing the need for an artificial hip replacement now and in the future. Learn more about CHOP’s hip experience, expertise and comprehensive care.  
Ortho patient Ella with US News 2024-25 Badge

Why choose CHOP

CHOP’s Hip Preservation Program focuses on hip conservation in young adults to stop continued damage and prevent the need for premature hip replacement.

Related specialties and programs

Young Adult Hip Preservation Program

Hip Disorders Program

Orthopedic Center

Sports Medicine and Performance Center

Resources to help

Young Adult Hip Preservation Program Resources

We have created resources to help you find answers to your questions and feel more confident in decisions you make about treatment.
Female doctor helping teen girl with hip injury.

Meet your team

Our team of hip specialists is actively researching the conditions that cause hip deformities, investigating new surgical techniques and tracking long-term outcomes for patients with hip disorders.

Patient stories
Our Stories
When Morgan was 11, longstanding hip issues began to severely limit her mobility and ability to play her favorite sport, soccer. Here, she describes the experience in her own words.
View all patient stories