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What is FAI syndrome?

Femoroacetabular impingement (FAI) syndrome is a disorder of the hip that typically affects young adults. It is the result of an abnormal contact between the femur (thigh bone) and the acetabulum (the socket).

Hip Structure

The hip is a ball and socket joint made of a femoral head (ball) and an acetabulum (socket). The hip is surrounded by groups of muscles and ligaments that support the bones. The surface of the femoral head and acetabulum are covered with a smooth cartilage allowing the two surfaces to glide over each other. At the edge of the acetabulum is another cartilage called the labrum.

Diagram of Hip Joint

What Causes FAI Syndrome?

Patients with FAI syndrome have a characteristic hip shape; either cam or pincer morphology. Patients with FAI syndrome also have alterations in the way their muscle control their hip. The combination of these two issues results in an abnormal contact between the femur (thigh bone) and the acetabulum (socket) which is painful.

A cam hip shape is characterised by a femoral head that is oval shaped rather than round. A pincer hip shape is characterised by a socket that is deep. Many people have cam and or pincer hip shapes without them causing problems.

How is FAI syndrome diagnosed?

FAI syndrome is diagnosed by understanding patients' symptoms, by examining them and by looking at their hip X-rays and or scans (CT or MRI).

Patients typically describe hip or groin pain that is related to a movements or a certain position. The pain may also be felt in the back, buttock or thigh. In addition to pain, patients may also describe clicking, catching, locking, stiffness, restricted range of motion or giving way.