Loosened hip replacement. Coloured computed tomography (CT) scan of the pelvis of a patient that has had a hip replacement. The prosthetic joint consists of a shaft and ball attached to the top of the femur (thigh bone) and a socket that is inserted into the pelvis. The socket has become loose and there is a gap between it and the bone (indicated by arrows). This may be caused by an infection, injury, or further deterioration of the underlying bone. Treatment is with replacement of the socket.