Femoral-acetabular impingement (FAI)
In femoral-acetabular impingement (FAI), the hip joint isn’t shaped normally. This causes the bones to rub together and limits normal range of motion. It also causes pain when moving.
FAI caused by an improperly shaped thigh bone is called cam impingement. This happens when the head of the thigh bone isn’t completely round. Certain movements make it catch against the edge of the socket, damaging the cartilage and lining of the hip socket.
FAI caused by an improperly shaped socket is called pincer impingement. It happens when extra bone grows in the socket or when the socket isn’t angled properly. This causes the socket and the thigh bone to rub together.