This article describes the corrosion resistance and ion release from main transition metallic bearings used as medical devices. It discusses the main issues associated with the in vivo presence of ions and their biocompatibility during the exposure of patients to different aspects of ion toxicity. These include ion concentration and accumulation in organisms, reactive oxygen species and oxidative stress, and carcinogenicity stimulated by the corrosion process and toxic ions release.

The interaction of an implant with the human body environment may result in degradation of the implant, called corrosion. This article discusses the corrosion testing of metallic implants and implant materials. The corrosion environments for medical implants are the extracellular human body fluids, very complex solutions containing electrolytes and nonelectrolytes, inorganic and organic constituents, and gases. The article describes the fundamentals of electrochemical corrosion testing and provides a brief discussion on various types of corrosion tests. It illustrates corrosion current density determination by Tafel extrapolation, potentiodynamic measurement of the polarization resistance, electrochemical impedance measurement, and potentiostatic deaeration. Tests combining corrosion and mechanical forces, such as fretting corrosion tests, environment-assisted cracking tests, and ion-leaching tests are also discussed.