The hip is a ball-and-socket joint. Hip impingement can occur if the ball is too big or too misshapen to fit properly into the socket. It also can occur if the exterior edge of the socket extends to the point that it covers too much of the ball. In many cases, hip impingement is caused by a combination of these two problems.
Hip impingement can damage the labrum, the soft cartilage that rings the hip socket and helps hold the ball in its proper place.