The invention relates to a device which is used for solidly connecting an acetabular cup shell to bone using at least one screw. According to the invention, the screw passes through a hole housing a ring mounted in the shell of the acetabular cup. The ring is mounted within an aperture of the shell and can be rotated therein about the longitudinal axis of the screw. The ring is a split-ring comprising a non-circular outer profile which co-operates with the non-circular profile of the hole which is disposed in the shell. In this way, when the ring is rotated in the hole and wedged in place therein, it is constricted thereby locking the screw to the shell in the desired position. Alternately the screw can have an enlarged thread adjacent it's head end to expand an internally threaded split-ring.