The second generation Metal-on-Metal (MoM) hip replacements have been considered as an
alternative to commonly used Polyethylene-on-Metal (PoM) joint prostheses due to polyethylene wear
debris induced osteolysis. However, the role of corrosion and the biofilm formed under tribological
contact are still not fully understood. Enhanced metal ion concentrations have been reported widely
from hair, blood and urine samples of patients who received metal hip replacements and in isolated
cases when abnormally high levels have caused adverse local tissue reactions. An understanding of
the origin of metal ions is really important in order to design alloys for reduced ion release. The welfare
of patients and concerns of hypersensitity and other potential side effects have been recognised by
both patients and surgeons. Both simple reciprocating pin-on-plate wear tests and hip simulator tests
have been carried out to characterize the relationship and interactions between electrochemical
reactions (corrosion), mechanical damage (wear) and biological environments. It was found that metal
ions originated from two sources: (a) depassivation/repassivation of the contacting surfaces due to the
interaction with tribology and corrosion processes under simulated motion and load and, (b) corrosion
of nano-sized wear particles generated from the contacting surfaces.
Keywords: tribology, hip prostheses, protein, synovial fluid, wear, ions release