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Leaflet: Femoroacetabular impingement

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Last updated: March 2019

Femoroacetabular impingement

What is it?

FAI occurs when the space between the ball (femur) and socket (acetabulum) in your hip joint is narrowed and the surrounding soft tissues become pinched.

What are the symptoms?

Pain can follow trauma but often arises with no clear cause and can progress with time. Pain is felt mostly into the groin although can also be felt on the side of the pelvis. There can be a background ache felt but the greatest complaint is often a sharp or catching sensation in certain positions. More painful activities tend to be when flexing the hip or twisting the hip. Examples may include, although are not limited to:

  • sitting on a low chair
  •  putting on shoes and socks
  •  getting in and out of the car
  •  change of direction at speed when playing sports.

How does it happen?

There are four potential causes of FAI, often with more than one occurring simultaneously:

  1. Poor muscle balance – in this scenario it is not the shape or structure of the joint causing the problem but in fact the way the joint is moving. In this scenario the ball will sit towards the front of the socket and this reduces space on movement.
  2. Labral tear – surrounding the rim of the socket there is some thick cartilage called fibro cartilage which amongst several functions serves to deepen the socket. If there is a traumatic onset associated with a weight bearing twisting injury to the hip its is possible to tear the labrum.
  3. CAM impingement – The shape of the ball and socket joint is shown in the image overleaf. In this scenario the femoral neck is thickened and so on bringing the hip up comes into contact with the socket more rapidly.
  4. Pincer – this is opposite of a CAM impingement; here there can be small bony projections called osteophytes from the edge of the socket bringing the rim of the socket closer to the ball.

How is the diagnosis of FAI made?

The diagnostic process consists of three parts:

  1. A series of questions to establish a pattern about your symptoms. This will include details about where you experience pain and when it is good and when it is bad.
  2. Clinical tests – the clinician will ask you to move your hip and may also move the hip around themselves. They will try and seek to find what movements are restricted and/ or painful.
  3. Radiography – X-rays can be useful in diagnosing a CAM or pincer lesion. If a labral tear is suspected an MRI may be required. Sometimes labral tears cannot be seen on MRI and so a dye will need to be injected into the joint prior to the scan to ‘highlight’ any lesion. This is called an MRA. The clinician will be able to discuss which images are appropriate for you based on the clinical examination.

What treatment options are there?

As noted above it is thought that often there is more than one factor contributing to FAI symptoms. Since some people with CAM and pincer lesions do not experience pain it cannot be guaranteed that if these are found that they actually contribute to the pain. It is therefore believed that in most, if not all cases the biomechanics of the hip (how it moves) will play a role. For this reason the first line of treatment for almost all cases should be physiotherapy.

Physiotherapy can be challenging initially and can even cause some pain. The aim of physiotherapy will be to correct muscle imbalance (strengthen weak muscles and stretch tight muscles and soft tissues). The main part of physiotherapy will be a home exercise programme, however on occasion additional treatments may be needed. If this is the case your physiotherapist will explain these fully in advance to ensure you are happy to proceed.

Sometimes pain severity can necessitate a pain killer prior to being able to take part in physiotherapy. This can be oral medications such as paracetamol, NSAIDS e.g Ibuprofen or even weak opiates such as Codeine and Tramadol. An alternative would be a joint injection of corticosteroid and local anaesthetic.

Joint injections have been shown to give symptoms relief for up to six months in FAI. Due to the nature of the hip joint they will need to be completed with fluoroscopic guidance so are undertaken in the radiology department. Since this is an invasive procedure there is some risk involved and may not be appropriate for everybody. Therefore if this is considered you clinician will discuss pros and cons with you as well as the contraindications. If it is deemed appropriate a referral can be made to your local radiology department.

Finally, if all conservative measures have failed to improve your pain there are surgical management options. If this is required your clinician can discuss the referral process with you. However since conservative measures are often very effective and carry less risk, they should be trialed for a minimum of three months prior to consideration of surgical management.


Exercise to manage FAI will depend on contributing factors and so will be tailored to the individual during physiotherapy sessions. Below are some exercises you can start in advance of your physiotherapy sessions.

Lie on your back with your knees bent to 90 degrees and feet on the floor shoulder width apart.

Engage your core muscles and slowly lift and lower your hips off the floor. Repeat 10 times.

Hip flexor stretch:
Half kneeling as in the picture. Push pelvic forward keeping frame upright. Hold 10-20 sec. repeat 5 times

What if my pain doesn’t resolve?

If you have followed at least a three month course of conservative management as detailed above, and have a clinical history and radiological evidence of FAI your clinician will discuss invasive measures in more detail with you. If this is necessary you will be referred to an orthopaedic surgeon. You may request a specific hospital or surgeon if you prefer but otherwise you will be referred using the e-referral system allowing you to choose where and when you will be seen.

For further information about hip pain and exercises, visit Versus Arthritis.