The prosthesis replaces the articular surfaces and creates a biological and mechanical interaction with the bone. In order to optimize the bone–prosthesis ratio, over the years the surgical technique, the fixation of the bone prosthesis (cementation or biological fixation), the design, the geometry of the prosthetic components, the biomaterials have been improved. The prosthetic articulation acquires a "new normality" and there is a link with the "disease of the prosthetic joint". The nosographic profile, the pathogenetic mechanisms, the clinic and the medical–surgical therapy are becoming increasingly clear. The control over the years of a prosthetic implant consists therefore in the monitoring of the bone metabolism.