Femoroacetabular Impingement (FAI)

Understand everything about your condition

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Femoroacetabular impingement (FAI) is a condition caused by abnormal contact in the hip joint. The hip joint is shaped like a ball and socket. The “ball” is the femoral head (the top of the thigh bone/femur) and the “socket” is the acetabulum (pelvis), which is shaped like a cup. The hip also has two layers of cartilage, the rubbery tissue, to help the bones move smoothly over one another. These are known as articular cartilage, which lines the ball and socket, and labrum cartilage, which forms a cushioning ring around the pelvis, acting as a seal and securing the femoral head in place.

People with FAI have extra bone growth either around the femoral head or the rim of the acetabulum, or both. This causes friction and abnormal pressure on the bones and cartilage, meaning they “wear out” more quickly. In medical terms, impingement means “friction between joints” or “soft tissue compression”. All hips impinge, but in FAI this occurs at an earlier angle, leading to pain and movement issues, as well as risking early osteoarthritis development. It is thought that many people have this extra bone growth, however not all will develop FAI.

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There are three types of FAI:

  • Cam type: extra growth on the femoral head that rubs the acetabulum and the articular cartilage. This type is more common in young, athletic men.
  • Pincer type: an over-sized pelvis that causes friction on the femoral head and can damage the labrum cartilage. It is less common overall, but occurs more in middle-aged women.
  • Mixed type: a combination of both Cam and Pincer.

  • Causes


    The reason FAI occurs can vary and, for many patients, no obvious cause can be found. FAI is more likely to appear in young athletic people and may be related to repetitive movement, especially squatting. Other repetitive movements, such as getting in and out of cars, or activities that cause the hip to move abnormally, can contribute. It may be due to a combination of hip development issues and then exercise or movement later on, provoking the hip.

    As well as being young or athletic, males and Caucasians are more at risk. It is thought there may be a genetic link, although this is not yet proven.

  • Symptoms


    FAI is the most common cause of hip pain in young and middle-aged adults. It can occur quickly, often after injury, or gradually, often after prolonged exercise. Pain is the most common symptom of FAI and can develop in various places, making diagnosis difficult. Pain most commonly occurs in the lower groin, but can also be present in the lower back, the side of the affected hip, the upper leg or beneath the buttocks. Sitting cross-legged or sitting for long periods may initiate it.

    Another symptom of FAI is reduced range of motion or movement that causes pain. Usually, the easiest way to recognise impingement is when pulling the knee to the chest, known as hip flexion. Less commonly, a periodic “clicking” may occur or feeling as if the hip is coming out of the joint.

  • Diagnosis


    As above, diagnosing on pain symptoms can be challenging due to the range of places symptoms can occur. Historically, FAI was often misdiagnosed as groin strain or hernia or was missed entirely, however there is now much more awareness of the condition.

    Diagnosis will typically involve taking your medical history and an evaluation of your activity, including childhood. A physical examination will see how the hip appears (swelling, bruising, etc.) and will involve an impingement test (i.e. the FADDIR test). For this test, the doctor will bring your knee up towards your chest and then rotate it inwards towards your opposite shoulder to see if the hip pain is recreated. The tests vary in their efficiency for supporting diagnosis, however restriction on inwards rotation or flexion abduction (moving the knee towards the chest and outwards) is often most useful. An x-ray may be used to examine the bones, the space between them and to help assess if any damage has occurred. MRI (magnetic resonance imaging) and CT (computerised tomography) scans are not common for diagnosing FAI, but an MRI may be used to check damage to the cartilage or to help build a 3D model of the hip, if needed.

  • Non-Surgical Treatments


    Non-surgical management is the first line of treatment for FAI and include:

    • Painkillers or anti-inflammatories: these can be bought over the counter but, if needed on a long-term basis, should be discussed with a doctor.
    • Injections:
      • Corticosteroids: cortisone-like medicines used to provide relief for inflammation.
      • Hyaluronic acid (viscosupplements): artificial synovial fluid, which may preserve cartilage.
    • Physiotherapy: physio programmes can include muscle strengthening and a focus on activities that avoid pain and enhance mobility, however, the effectiveness of such programmes for managing FAI is questionable and still being researched.

    While conservative treatments may help for a limited period, FAI will invariably lead to the need for surgery, especially to avoid complications, such as osteoarthritis.

  • Surgical Treatments

    • Hip Arthroscopy: Arthroscopy is a form of minimally-invasive surgery, meaning it uses small tools and incisions (cuts). The procedure involves using a small camera, called an endoscope, and fine tools in the hip to treat the damaged tissues and correct the bone deformity - a process called “debridement”. FAI is the most common reason for hip arthroscopy and often includes the repair of a tear in the labrum. Recovery is generally several months with the use of crutches; physiotherapy and hydrotherapy may be recommended. This kind of procedure can be highly successful and even elite athletes may find they can return to their previous exercise. As well as easing pain and freeing movement, an arthroscopy may also help to prevent osteoarthritis development. It is usually performed as a “closed” operation, meaning smaller incisions. However, if the damage or impingement is more severe, an “open” operation may be required, which will mean larger incisions and longer recovery time. Learn More
    • Hip Resurfacing: This procedure trims down the damaged area of the femoral head and covers it with a cap made of smooth metal. The acetabulum has the damaged bone and cartilage removed and is lined with a metal surface. Advantages of this surgery are that the implant may last up to 20 years and has a reduced risk of hip dislocation when compared to a total hip replacement. However, there is a risk of a “local tissue reaction” from the two metal surfaces, which can lead to pain, swelling and possibly the need for further surgery. For this reason, the procedure is being performed less than it used to be.
    • Total Hip Replacement: A total hip replacement is an operation that uses two implants to replace the damaged hip joints. The surgeon makes an incision (cut) in the hip, removes the damaged tissues and replaces them with artificial ones known as a “prosthesis” or “implant”. The femoral head replacement is a metal or ceramic ball with a metal stem. The pelvic cartilage surface is replaced with a metal “socket”, then screws or cement are used to hold it in place. A total hip replacement typically involves spending up to 4 days in hospital, a tailored physiotherapy programme and a recovery period that includes time using a frame or crutches. For younger patients who are still growing, the joint may need to be replaced at a later date. A second hip replacement, also called “revision surgery”, can be a more complex procedure and it is therefore important that patients choose a surgeon with the right experience. Learn More


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