Abstract: The invention relates to a joint prosthesis with a cap having a supporting surface, a telescopic arrangement having a telescopic component on a cap side and a telescopic component on a holder side and connected to a holder for securing to a bone surface, wherein the supporting surface is formed by an inner surface of the cap which is at least approximately shaped to fit the bone head. A restricting device acts dependently upon the direction so as to allow the cap to be moved in relation to the holder in a direction away from the socket and to prevent or at least hamper movement towards the socket. Also disclosed is a surgical device for making a drilling with a bush to accept an instrument and a system connected to the bush to accept the joint head at least partially; the median longitudinal axis of the bush is brought into relation with the periphery of the joint head in order to facilitate the positioning of the device in relation to the bone system.