Abstract: The external surface of the hip joint socket is provided with a contrast ring in a diametric plane of the joint head receiving cavity as well as with a metallic measuring ring in the upper surface of the socket body. The measuring ring is concentric to the axis of rotation of the body and is parallel to the plane of the contrast ring. By measuring the distance of the two metallic rings from each other in an X-ray picture, a determination can be made as to whether a displacement of the center of the spherical joint head is due in part to a cold flow of the socket material or exclusively to abrasion.