In some people the femoral head (ball part of joint) is not completely spherical. There may be a small ‘bump’ or ‘cam’ on the front of the femoral head. In certain positions this causes the side of the femoral head to rub against the socket. Similarly, if there is too much coverage of the head by the socket this can also cause ‘pincer’ impingement. Over years both forms of impingement will lead to damage which starts off as a tear of the labrum, then progressing to damage of the articular cartilage (smooth lining of joint). This eventually results in arthritis. Patients classically develop symptoms in their 30’s and 40’s and this is a common cause of arthritis in the younger age groups.