The hip joint is a ball-and-socket joint, and a normal hip has a perfectly round ball (femoral head) and a socket (acetabulum) that matches it and is concentric.  Any bony abnormalities of the ball or socket can lead to bony impingement and injury to the cartilage and labrum.  The most common form of hip impingement is cam impingement, where the ball is not perfectly round.  Typically, a bump or flattened aspect of the ball is forced into the joint, causing impingement, a labral tear, and cartilage damage.  If initial attempts at non-surgical treatment fail to alleviate pain and limited function, hip arthroscopy may be recommended. Cam impingement can be properly treated with surgery, including hip arthroscopy for the vast majority of cases, and occasionally a surgical dislocation of the hip.  Surgically, the cam (bump) is resected using a motorized burr to remove bone.  A portable x-ray machine is used to ensure the proper amount of bone is removed and to help reestablish the round, spherical shape of the femoral head (ball).  Once adequately resected, the hip no longer impinges during motion and activity.  Rehabilitation from a labral repair typically follows the same outline in the hip arthroscopy section and is modified as needed.