The present invention relates to a an attachment device for attaching a prosthesis to a bone, comprising: a base plate having an extension in an xy-plane; a first holder for holding a first abutment; a second holder for holding a second abutment; a locking plate attached to the base plate to restrict movement of the holders in a z-direction away from the base plate. The locking plate is configured to allow rotation of the first and second holder around a z-axis perpendicular to the xy-plane. The locking plate and the base plate is configured to allow movement of the first holder along the x-direction and to prevent movement the y-direction and to prevent movement of the second holder in the x- and y-direction. At least one flexible member is arranged between each of the first and second holders and the base plate, the flexible member being flexible in the z-direction to allow movement of the first and second holder in the z-direction and to allow the first and second holder to tilt with respect to the xy-plane.