A design method for design of a rig is presented. The rig comprises a hollow tubular shell, and the interior of said shell defines at least first and second intersecting cylinders, and a movable wall insert, configured to fit inside the hollow tubular shell so that a bore in the insert defines an active guide channel in the form of a first cylinder, wherein another active guide channel in the form of a second cylinder may be formed by moving the movable wall insert to another position inside the hollow tubular shell. The design method comprises identifying a damage area, presenting a 3D view of identified damage area and generating a 3D model of a virtual rig. The generating comprises virtually placing in 3D view a shape covering or partly covering damage area, and creating, based on the position of the virtually placed shape, a position of hollow tubular rig shell of the virtual rig. The method further comprises selecting the at least first and second intersecting cylinders of the virtual rig, based on the size and form of the virtually placed shape, designing the movable wall insert to mimick parts of the pattern of the guide channel inside area of the rig, and creating a positioning surface of the virtual rig which is a bone and/or cartilage-engaging end of hollow tubular shell. The positioning surface is adapted to follow the surface surrounding the virtually placed shape when the virtual rig is placed in a virtual model of the joint. The method comprises producing a rig according to the virtually created rig.
