Hip impingement Femoroacetabular impingement / FAI

An impingement means "wedging". In hip impingement, a ring of connective tissue or the hip cartilage becomes wedged between the femoral head and the hip socket. This causes pain in the hip.

Hip impingement is also called femoroacetabular impingement, often abbreviated as FAI.

The hip joint consists of a femoral head and a hip socket. The head and the socket are covered by a thin, smooth layer of cartilage that ensures that both parts of the joint can glide over each other. Along the edge of the hip socket is a ring of connective tissue called the labrum. The labrum keeps the femoral head better positioned in the hip socket.

Normally, the hip joint consists of a rounded femoral head and a deep hip socket. The curvature of the femoral head fits perfectly into the curvature of the hip socket. In the case of hip impingement, the shape of the femoral head or the hip socket is different. This means that the head and the socket no longer fit together properly. As a result, the cartilage and the labrum can become wedged. We feel this as pain in the hip or groin.

There are three types of hip impingement. The different types describe the joint shape of the femoral head and the hip socket.

Cam impingement

In this case, the curvature of the femoral head is not round enough, so that it becomes too large for the hip socket.

Pincer impingement

In this case, the hip socket has a defect. The edge of the hip socket protrudes too far, making the socket too deep. This can cause the femoral head to collide with the edge of the hip socket during movement.

Combined (mixed) impingement

This is a combination of a cam impingement and a pincer impingement. Both anomalies are present.

The misalignment of the hip joint in itself does not cause any symptoms. However, if the misalignment causes damage to the cartilage or the labrum, complaints may arise.

Damage to the cartilage or the labrum is caused by the femoral head and hip socket colliding frequently and under the action of strong forces due to the misalignment. Because the hip joint is protected by the cartilage and the labrum, these get damaged first.

The abnormal shape of the joint is usually congenital. A deviation of the hip joint can also occur after a broken hip (online physiotherapy check or make an appointment with a physiotherapy practice in your area.

Magee, D.J., Zachazewski, J.E., Quillen, W.S., Manske, R.C. (2016) Pathology and intervention in musculoskeletal rehabilitation Elsevier, 2nd edition.
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Philippon, M.J., Brian Maxwell, R., Johnston, T.L., Schenker, M. & Briggs, K.K. (2007) Clinical presentation of femoroacetabular impingement Knee Surg Sports Traumatol Arthrosc. 2007-15:1041–1047.