Wear analysis of materials used as orthopaedic implants

In the biomedical field, about 6% of the hip total prostheses must be replaced after 9 years. One of the main causes of the aseptic loosening may be attributed to fretting corrosion between the prosthesis and the bone cement. To understand this degradation, a fretting test between a stainless steel, 316L and PMMA has been used in Ringer solution. Fretting maps for the contact 316L/PMMA were determined in air and in Ringer solution. It has been shown that the lubricant effect of the aqueous environment shifts the gross slip/partial slip transition towards larger normal forces or lower displacements.To understand the fretting degradation behaviour of 316L against PMMA, fretting corrosion experiments have been investigated under constant applied potential. The first conclusion is that the dissipated energy is maximum at about −600 mV/SCE. The wear on PMMA does not depend on the applied potential. Moreover, the wear coefficient is lower than that in air due to the lubricant effect of the Ringer solution. Wear on 316L depends on the applied potential. The wear volume is minimum at −600 mV/SCE although the dissipated energy is maximum. The wear on 316L in Ringer solution is attributed to a dissolution process due to the local destruction of the passive film by fretting. The effect of potential on the wear of 316L may be accounted for by changes in the aqueous environment confined in the contact zone due to a restricted mass transport from the bulk solution and to the large local current densities consecutive to the destruction of the passive film. Accordingly, the wear volume on 316L is correlated to the time. Finally, the proton reduction, inside the contact, is believed to contribute significantly to the dissolution process.