Femoroacetabular Impingement (FAI)

Hip impingement syndrome, or femoroacetabular impingement, has only recently become a recognised cause of hip pain in young adults.

Prof. Reinhardt Ganz, Professor of Orthopaedic Surgery in Bern, Switzerland, first described the condition in the 1990's. He first recognised this condition in some patients who had had surgical correction of hip dysplasia by a periacetabular osteotomy. In some of these cases he had performed an over correction. This lead to the hip joint going from being under-covered preoperatively to over-covered postoperatively. He later went on to recognise that the condition could occur primarily, particularly in young males, or labourers.

Hip impingement syndrome is at the other end of the spectrum from hip dysplasia where the coverage of the hip socket is insufficient.

Types of Hip Impingement

1. CAM Impingement

The normal hip joint has a recess at the junction of the femoral head and neck. (see diagram FAI-1) . With CAM impingement there is a loss of this of the normal femoral head/neck recess. Its junction is often filled in with a bony bump. With CAM impingement, the bump becomes jammed in front of the socket (acetabulum) as the hip goes into deep flexion. This abnormal shear force will cause either tearing of the acetabular labrum or adjacent articular cartilage within the hip socket.

2. Pincer Impingement

This occurs when the socket is excessively deep, particularly in the front (anteriorly). In normal hip joints the acetabulum is tilted slightly forwards to allow greater clearance of the hip joint in flexion. In about 6% of patients the acetabulum is retroverted (tilted backward), which will make impingement more likely (see diagram FAI-2).

3. Combined Impingement

The majority of patients presenting with this condition have a combination of both CAM and Pincer impingement.

Causes of Femoroacetabular Impingement

The exact cause of femoroacetabular impingement is unclear. It is thought that it is developmental (either present at birth or developing during childhood). There are some cases that may be due to a previously unrecognised slipped upper femoral epiphysis, which occurs during early adolescence.

Clinical Features

Patients will often complain of intermittent groin pain, sometimes radiating into the buttock. It is worse after exercise or heavy lifting. It sometimes can be associated with a catching sensation. Clinical examination usually reveals limited flexion, as well as internal rotation of the hip. This movement will often cause groin pain. This provocative test is called the impingement test.


Plain x-rays do not always demonstrate abnormalities. To make the diagnosis sometimes a CT or MRI scan is required to both confirm the condition and adequately assess the type of impingement that is present.


Conservative treatment can ameliorate some of the symptoms associated with this condition.

1. Activity Modification

Simple analgesia, Pilates and ergonomic advice will often be helpful in reducing the level of symptoms. However, the condition is usually progressive and surgical treatment is often required.


1. Open surgery with dislocation

The bump at the femoral head/neck junction can be excised to restore the normal concavity (see diagram – FAI-3) . This procedure allows good exposure of the acetabulum and any over coverage of the anterior acetabulum can be removed and combined with repair of the acetabular labrum at the same time. This allows for treatment of the Pincer impingement by removing excessive bone from the anterior acetabulum.

2. Mini anterior incision

An incision less than 10cm can be made over the anterior aspect of the hip joint and the femoral head and neck exposed without the need for hip dislocation. A good view of the femoral head and neck can be achieved, but it is a little more difficult to obtain exposure to the acetabulum compared with the open dislocation technique. It does however allow a more rapid recovery than the first method.

3. Arthroscopic hip debridement

This procedure has recently been developed. It is technically very demanding and requires particular expertise in this technique to perform it adequately. There is little published data regarding the effectiveness of this form of surgery.


Surgical treatment of femoracetabular impingement has produced very good results where it is performed before significant osteoarthritis has developed. In theory, early treatment of hip impingement syndrome will hopefully reduce the need for subsequent hip replacement, but so far there has been no published data to confirm this hypothesis.

If a patient presents with this condition and significant osteoarthritis is present, then non-operative management is recommended until the symptoms are severe enough to warrant total hip replacement.

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