The invention relates to an operation system comprising at least one implant and means for the fastening of the implant to a bone, wherein the fastening means include at least one solid spacer, which can be formed of hardened bone cement and is arranged between the implant and the bone in the implanted state, and hardenable liquid bone cement which can be introduced into hollow spaces or intermediate spaces present between the spacer and the implant and/or between the spacer and the bone and wherein the spacer, on the one hand, and the liquid bone cement, on the other hand, are provided with contrast agents chosen in dependence on an imaging observation process or inspection process, in particular an X-ray process, to be used in or after the operation such that the spacer and the liquid cement can be distinguished from the surroundings and from one another on the observation or inspection of their position, in particular in an X-ray.