hip specialties

About Femoroacetabular Impingement (FAI)

Pain in the front part of the hip after prolonged sitting or walking may be caused by femoroacetabular impingement. This disorder is caused when the ball of the femur does not have full range of motion in the hip socket because there is too much bone around the femoral head, which causes pain. Or the hip socket may be turned backwards (retroversion) and the femur bumps into the socket (acetabulum). It is possible for both to occur.

FAI is a process that can go on in the hip joint due to abnormal shape of the ball and socket. This condition can cause pain when the individual sits or stretches. It can be caused from retroversion of the acetabulum or an abnormal shape to the front of the femoral head and neck (top of the thigh bone), or, in about 80 percent of cases, a combination of both.

A hip with a bump or not enough offset between the head and the neck (as seen on the left) can force its way into the hip joint, moving the labrum out of the way and then cause damage to the cartilage lining the socket. It acts like a “cam” (seen on the left in diagram B).

On the right, when the socket is too deep or it is facing backwards, the head gets pinched and the labrum often gets damaged and a ridge or divot can form on the neck (seen on the right in diagram B).

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Frequently Asked Questions About Femoroacetabular Impingement & Surgery

What is femoroacetabular impingement?

Impingement occurs when the ball (femoral head) doesn't have full range of motion in the socket (acetabulum). This is caused by too much bone around the femoral head and/or the socket turned backwards (retroversion) and the femur bumps into the rim of the acetabulum and causes pain and possibly damage over time.

What are symptoms common with impingement?

Impingement can show at any age between 20-50 years old. Most of the time, people will start to get pain in the front of their hip (groin) after prolonged sitting or walking. Walking uphill can also be difficult. Sometimes they feel a dull ache in the groin, other times catching or popping.

What happens inside a hip with impingement?

When the extra bone on the femoral head and neck (ball) hits the rim of the acetabulum (socket) the cartilage and labrum can be damaged. These tissues are the cushion between the ball and socket (clear space on X-rays), and when damaged can cause pain and start to degenerate (get small tears and form arthritis). If left untreated, pain and arthritis continues, and usually a hip replacement (total hip arthroplasty) is needed at some point.

What does retroversion mean?

Retroversion is a form of acetabular dysplasia where the socket is facing more backwards than it normally would, which can cause the femur (thigh bone) to bump into it when you flex your hip. This happens because the front of the socket (anterior wall) is lower than the back of the socket (posterior wall). It can be seen by subtle shadows on X-ray. Anteversion means facing forward, and this is normal.

How do I know if I need surgery?

A specialist may recommend surgery if you have pain that is in the front groin (anterior) that affects daily activities and prevents you from doing the things you want to. If X-rays show extra bone around the head/neck with early degenerative changes (mild arthritis) but evidence of possible good cartilage, you may be a candidate for a femoracetabular debridement. If there is retroversion of the acetabulum (socket) and that seems to be contributing to the impingement, you may need a periacetabular osteotomy with or without a femoral head debridement.

What is involved in a femoroacetabular debridement?

Usually a femoroacetabular debridement is a surgery through an incision over the side of your hip where the surgeon removes the bone and damaged tissue.

What is involved in a periacetabular osteotomy (PAO)?

The surgeon goes through an incision over the front of the hip, then, with X-ray guidance (fluoroscopy), carefully cuts through the three pelvic bones (ischium, pubis, ilium) around the acetabulum to free it from its original position. Once the acetabulum is in its new location (facing the right direction with good coverage), we fix it there with screws (usually three to six). From this same incision we can access the hip joint to debride extra bone from the head/neck as needed.

Will I need a blood transfusion?

You may. We recycle the blood you lose at surgery and give it back to you if there is enough. But sometimes you will need a transfusion of one to two units after surgery. You may donate your own blood if you are able, but if not, the blood bank is very safe, and we can use that if it's needed.

How long will I be in the hospital?

Usually, the hospital stay is two to three days after surgery.

What physical therapy do I have to do?

Starting the day after surgery you will have physical therapy twice a day that includes gentle exercises and learning to sit, stand, and walk with partial weight-bearing and crutches. You may take a few steps the first day around your room and then into the hallway on the second day. After you leave the hospital, the important therapy you have to do is walk, rest and let your surgery heal.

What are the major risks to the surgery?

The major risk include the following:

  • Blood clot We reduce risk of this by using a blood thinner, TED hose (compressive stockings) and compression boots on your feet to increase circulation.
  • Infection You are given IV antibiotics before surgery, which is continued for one day after, and then keep a close watch of the incision for redness or drainage.
  • Failure to heal This is uncommon but always a concern, especially if you smoke. If the bone doesn't heal, the screws can break and the bone can move. An additional surgery to increase bone healing could be needed, but very rarely.
  • Avascular Necrosis This is uncommon, but possible. If the blood supply to the femoral head is damaged, the bone may collapse and die. This could speed up the need for a total hip replacement, if it were to happen.
  • Nerve Palsy from PAO A sensory nerve called the lateral femoral cutaneous nerve is right where we do surgery. We do our best to identify it and protect it but there is a 50% chance you will have some numbness over the front of your thigh; over time sensation usually returns.

What happens when I leave the hospital?

You will usually need 24-hour help for a week. If you don't have adequate help at home, you could consider a rehabilitation center. The final plans will be made while you are recovering in the hospital.

What do I do at home while recovering?

First six weeks: You will finish taking blood thinners (aspirin for six weeks); wear TED hose; walk with two crutches (partial weight bearing); keep the wound clean.

Next six weeks: You will transition to one cane or crutch as instructed by your physician until three months after surgery; you may start gentle stretching or strengthening exercises; walk.

After three months: You may return to work part time or full time as tolerated (two to three months from surgery), continue to walk and return to gentle exercise.

After six months: You may return to full activity (when the bones are completely healed) except for running/jumping activities. The best lifelong activities are walking, swimming and biking to preserve your hips’ health.

How long do I take narcotics?

Only as long as you need to, about seven to 21 days from surgery. Be aware that sometimes anti-inflammatories (NSAIDS) can slow down bone healing, but Tylenol doesn't.

When can I drive?

Usually three to four weeks after surgery.

When do I see my doctor after surgery?

You will probably have staples and should see your doctor in two weeks, then again six weeks after surgery for X-rays, then three months, six months, one year, and every year or two so we can see how your hip progresses.

Who do I call if I'm having problems after surgery?

Call the nurse/MA who works with your surgeon. Call the orthopedic clinic and ask for her voicemail; she will get back to you within a business day; otherwise, call the orthopedic resident on-call.

How long will it take to fully recover from surgery?

For debridement or periacetabular osteotomy, you will be walking within a couple days of surgery, on one to two crutches for three months, and it usually takes nine to 12 months to feel fully recovered.

How long with the surgery last? Will I need another surgery?

We hope to prolong the time between now and when you need a hip replacement. But the exact time in years is unknown, and on an individual basis, based on the amount of arthritis in your hip already.

What lifelong activities can I do or not do?

We advise patients to resume what they can tolerate, especially walking, swimming and bicycle riding. We discourage repetitive jumping, running and heavy manual labor and lifting. These activities tend to wear out the hip faster.

Stephen K. Aoki, MD

Patient Rating:


4.8 out of 5

Dr. Stephen K. Aoki, Associate Professor, specializes in hip and knee sports medicine. His clinical practice and research focus on both adult and pediatric sports injuries. Current interests include hip preservation/femoroacetabular impingement in the young adult, hip arthroscopy, the pediatric and adolescent athlete, ACL tears in children, patella... Read More

Jill A. Erickson, PA-C

Jill Erickson has worked with our Adult Reconstruction Surgeons since 1999, and with Christopher Peters, M.D. exclusively since 2003, with Joint Replacements as well as Hip Preservation procedures. She is an integral member of our University of Utah Center for Hip & Knee Reconstruction team and coordinates our research, surgical and clinical ou... Read More

Travis G. Maak, MD

Patient Rating:


4.8 out of 5

Dr. Travis Maak’s practice is focused on sports medicine and arthroscopic treatment of the hip, knee and shoulder. He is the Head Orthopaedic Team Physician for the Utah Jazz and Assistant Professor in the Department of Orthopaedics at the University of Utah. Dr. Maak is originally from Salt Lake City and a graduate from Stanford University. He com... Read More

Christopher L. Peters, MD

Patient Rating:


4.7 out of 5

Dr. Chris Peters, Professor, specializes in adult reconstructive orthopaedic surgery of the hip and knee. He performs routine and complex joint replacements and bioregenerative hip preserving operations. One of his specialties includes the treatment of hip pain in young adults from acetabular dysplasia and/or femoro-acetabular impingement with pelv... Read More

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