An accessory which is made as a positioning jig, wherein said accessory is provided with passages (25) for screws (22) that can be screwed in said implants (7), these passages (25) and said accompanying screws (22) having such a shape that when the screws (22) are tightened they can be forced into a specific position and an accessory in the shape of a drill jig (6) in which one or several ducts (9) are formed for drills, which are provided in the drill jig (6) in function of the computer planning
