what is fai
Femoroacetabular Impingement (FAI) Femoroacetabular impingement (FAI) is a condition where the bones of the hip are abnormally shaped. Because they do not fit together perfectly, the hip bones rub against each other and cause damage to the joint. The hip is a ball-and-socket joint. The socket is formed by the acetabulum, which is part of the large pelvis bone. The ball is the femoral head, which is the upper end of the femur (thighbone). A slippery tissue called articular cartilage covers the surface of the ball and the socket.