warwick.ac.uk Introduction Femoroacetabular impingement (FAI) syndrome is increasingly recognised ... Previous hip injury such as acetabular fracture, hip dislocation or femoral neck fracture; ...

Normally, the ball glides smoothly within the socket, but a problem with the ball or socket rim can interfere with smooth motion, leading to hip impingement or femoro acetabular impingement (FAI).

So what we've gotten to understand is a concept of what we call "femoral-acetabular impingement," or "hip impingement," where the ball and the socket get a pinching with activity and range of motion.