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What is femoroacetabular impingement (FAI)?
Femoroacetabular impingement (FAI) is a hip condition where extra bone on the ball or the socket makes the two sides of the joint pinch together instead of glide. The ball is the top of the thigh bone; the socket is part of the pelvis. When they do not fit smoothly, the rim of the socket and its cartilage cushion (the labrum) take repeated hits. Over years, that pinching can wear the joint and cause pain.
Here is what I tell my patients. FAI is common. About 10 to 15 percent of adults have the bone shape that can cause it, though many never feel a thing. The trouble starts when that shape leads to pain, stiffness, or a torn labrum.
After more than twenty years treating hip and knee problems, I have learned that the hip is a great pretender. Groin pain, a catch when you sit, an ache after a long drive: these can all trace back to the same pinch. Naming it is the first step toward fixing it.
What causes hip impingement?
Hip impingement is caused by an irregular bone shape that forms during the growing years, not by anything you did as an adult. Most people are simply born with hips that are built to pinch. Exercise does not cause the condition, though hard training can make the symptoms show up sooner.
Doctors describe three patterns, based on where the extra bone sits:
- Cam type: the ball of the hip is not perfectly round. A small bump on the head and neck of the thigh bone grinds against the socket when you bend the hip. This pattern is more common in young, active men.
- Pincer type: the socket rim covers too much of the ball. That overhang crushes the labrum when you flex. This pattern shows up more often in active, middle-aged women.
- Combined type: both the ball and the socket are shaped abnormally. In my practice, and in the research, mixed cases are the most common of the three.
Some childhood hip problems raise the risk too, including a slipped growth plate (called slipped capital femoral epiphysis) and Perthes disease. Genetics play a part as well, which is why impingement sometimes runs in families.
What are the symptoms of femoroacetabular impingement?
The main symptom of femoroacetabular impingement is hip or groin pain that gets worse with bending, twisting, or long periods of sitting. Many patients trace a “C” shape with thumb and fingers over the front and side of the hip when I ask them to point to the pain. That gesture is so common it has a name: the C sign.
Watch for these signs:
- Groin pain, or a deep ache toward the outside of the hip
- A sharp catch when you squat, lunge, or get out of a low chair
- Clicking, popping, or a locking feeling in the joint
- Stiffness and less range of motion, especially turning the leg inward
- Pain after a long drive or a long meeting
The pain often starts mild and stays mild for years. Then it can turn a corner and start limiting sport, work, or sleep. Clicking or catching raises my suspicion for a labral tear, which is a tear in that cushion around the socket rim.
How is hip impingement diagnosed?
Hip impingement is diagnosed with a physical exam and imaging, usually starting with an X-ray of the pelvis and hip. In the exam, I bend the hip up, bring it across the body, and rotate it inward. If that recreates your pain, the impingement test is positive. This simple move is positive in the large majority of patients with true anterior impingement.
Imaging fills in the picture:
- X-rays show the bone shape and reveal cam or pincer bumps, along with any early arthritis.
- MRI shows the soft tissue, so I can see a torn labrum or worn cartilage. A dye injection into the joint can make small tears easier to spot.
- CT scans give a detailed 3D view of the bone when we need to plan carefully.
Sometimes I use a numbing injection into the joint as a test. If the numbing medicine relieves your pain for a few hours, that tells me the problem is truly inside the hip and not the back or the muscles around it. Sorting the source of pain matters, because groin pain can also come from the spine, tendons, or a sports hernia.
What are the treatment options for femoroacetabular impingement?
Treatment for femoroacetabular impingement starts with non-surgical care and moves to surgery only if the pain keeps limiting your life. Most patients begin with the same first steps, and many do well without an operation.
Non-surgical treatment for femoroacetabular impingement
In my practice, I start almost everyone here. The goal is to calm the joint and take stress off the injured labrum and cartilage.
- Activity changes: ease off the deep squats, long sits, and motions that trigger the pinch.
- Anti-inflammatory medicine: over-the-counter options like ibuprofen or naproxen can lower pain and swelling. Check with your own doctor before starting any medicine.
- Physical therapy: targeted exercises build the muscles that support and center the hip. Good therapy often buys real, lasting relief.
- Injections: a cortisone shot into the joint can settle a painful flare and, as noted above, help confirm the diagnosis.
Surgical treatment
When good non-surgical care fails and imaging shows real joint damage, surgery is worth discussing. The aim is to reshape the bone that is pinching and to repair the torn labrum. Most of this is done with hip arthroscopy, a minimally invasive method that uses small incisions and a tiny camera. The surgeon shaves the cam bump, trims the pincer rim, and fixes the labrum through those small openings. Studies report strong mid-term results, with more than 90 percent of hips doing well around five years after surgery.
Hip arthroscopy for impingement is a specialized hip-preservation procedure. My focus is hip and knee replacement, so when a patient is a candidate for arthroscopic impingement surgery, I make sure they see a fellowship-trained hip arthroscopy or hip-preservation surgeon for that specific operation. Getting the right surgeon for the right procedure is part of good care.
When does FAI lead to hip replacement?
FAI can lead to hip replacement when the impingement has already worn the joint down to arthritis. This is the point where I can help most directly. Once cartilage is badly worn, reshaping the bone no longer solves the pain, because the problem is now the arthritis itself.
Here is the honest part I share with every patient. Even with good treatment, impingement is a known risk factor for arthritis over time. Surgery early on may help symptoms and may slow the wear, but it cannot promise to prevent arthritis down the road. Some people with long-standing impingement do eventually develop end-stage arthritis and become candidates for hip replacement.
When that day comes, joint replacement is one of the most reliable operations we offer. I perform more than 700 hip and knee replacements a year, many using the Mako® robotic-assisted platform for precise implant placement. If your impingement has crossed into arthritis, that is exactly the conversation I am built to have with you.
When should you see a hip specialist?
See a hip specialist if hip or groin pain lasts more than a few weeks, limits your activity, or comes with clicking, catching, or stiffness. The longer femoroacetabular impingement goes untreated, the more wear it can cause. Early evaluation gives you the widest set of options.
Here is what I tell my patients: you do not have to live with hip pain, and you do not have to jump straight to surgery. Start with a clear diagnosis. From there, we build a plan that fits your goals, whether that is therapy, an injection, a referral for hip-preservation surgery, or, if arthritis has set in, a joint replacement.
Dr. Cory Calendine is a board-certified, fellowship-trained orthopedic surgeon at the Bone and Joint Institute of Tennessee, serving Franklin, Nashville, Brentwood, Columbia, and the wider Middle Tennessee area. To have your hip pain evaluated, request a consultation with Dr. Calendine or call the office at (615) 791-2630.
This article is for educational purposes only and is not a substitute for professional medical advice. Always consult a qualified healthcare provider about your own symptoms and treatment. Individual results vary based on personal health circumstances.
References
- O’Rourke RJ, El Bitar Y. Femoroacetabular Impingement. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023. PMID: 31613479.
- American Academy of Orthopaedic Surgeons. Femoroacetabular Impingement. OrthoInfo. Reviewed 2024.
- Pun S, Kumar D, Lane NE. Femoroacetabular impingement. Arthritis Rheumatol. 2015;67(1):17-27. PMID: 25308887.
- Frank JM, Harris JD, Erickson BJ, et al. Prevalence of Femoroacetabular Impingement Imaging Findings in Asymptomatic Volunteers: A Systematic Review. Arthroscopy. 2015;31(6):1199-1204. PMID: 25636988.
- Nwachukwu BU, Rebolledo BJ, McCormick F, et al. Arthroscopic Versus Open Treatment of Femoroacetabular Impingement: A Systematic Review of Medium- to Long-Term Outcomes. Am J Sports Med. 2016;44(4):1062-1068. PMID: 26059179.
