Femoroacetabular Impingement (FAI)
Femoroacetabular impingement (FAI) is a condition in which extra bone grows along one or both of the bones that form the hip joint — giving the bones an irregular shape. Because they do not fit together perfectly, the bones rub against each other during movement. Over time this friction can damage the joint, causing pain and limiting activity.
In FAI, bone overgrowth — called bone spurs — develop around the femoral head and/or along the acetabulum. This extra bone causes abnormal contact between the hip bones, and prevents them from moving smoothly during activity. Over time, this can result in tears of the labrum and breakdown of articular cartilage (osteoarthritis).
Types of FAI
There are three types of FAI: pincer, cam, and combined impingement.
- Pincer– This type of impingement occurs because extra bone extends out over the normal rim of the acetabulum. The labrum can be crushed under the prominent rim of the acetabulum.
- Cam– In cam impingement the femoral head is not round and cannot rotate smoothly inside the acetabulum. A bump forms on the edge of the femoral head that grinds the cartilage inside the acetabulum.
- Combined-Combined impingement just means that both the pincer and cam types are present.