If the affected hip becomes stiff despite physiotherapy or if X rays show progressive deterioration further information can be acquired by examination under aneasthetic. This is done as a day case procedure and takes about 15 minutes. With the patient asleep dye can be injected into the joint to outline the true shape of the femoral head. The hip can then be moved under X ray control to determine whether the femoral head can be contained by the socket. On the basis of the arthrogram patients are advised to either continue non operative management or surgery (osteotomy).