An adaptor for fixing a medical apparatus to one or two support structures, wherein the adaptor is constructed in three parts from a bearing part and two support parts, wherein the bearing part can be connected to the medical apparatus, the first support part can be connected to a first support structure and the second support part can be connected to a second support structure, and the adaptor can assume at least three states, wherein: in the first state, the bearing part is connected free of clearance to the first support part only; in the second state, the bearing part is connected free of clearance to the second support part only; and in the third state, the bearing part is connected free of clearance to the first support part and the second support part.