Impingement is not usually caused by dysplasia, but it can be painful. The pain is more like a pinching pain in certain positions of sitting or hip movement like a high kick when dancing. Impingement is usually caused by an abnormal shape of the neck of the femur just below the head. It can also be caused by a socket that is too deep.
When the neck of the femur is too thick or the socket is too deep, then the neck hits against the rim of the socket and causes pain and deterioration of the labrum or hip joint itself.
The test for impingement is usually done by flexing the hip and then twisting the hip inwards to rub the femoral neck against the edge of the hip socket. If this causes the pinching pain, then the most likely cause is impingement.
Treatment is normally surgical and can sometimes be done through an arthroscope as a minimally invasive procedure. When the pinching is over a big area, then the hip needs to be surgically dislocated and re-shaped with the surgeon is looking directly at the exposed bone and the surface of the hip joint.