Tribology and corrosion in hip joint replacements: materials and engineering

Fundamental aspects of biomechanics, tribology, materials science and the biological environment in which joint replacements function have been outlined in earlier chapters. The fundamentals of tribology and corrosion are outlined and the significance of their synergy is emphasised. Application of these basic principles to joint replacements is complex, both in terms of modelling and simulation. Only steady-state elastohydrodynamic analysis of total hip joint replacements was available initially, but realistic, more comprehensive analyses for time-dependent situations are rapidly enhancing our understanding of tribological actions in such implants. The analysis is complex, since speeds, loads and lubricant properties all vary throughout each cycle. An introduction to corrosion is presented, together with the background to corrosion in metal-on-metal total hip replacements. Protective films formed naturally on metallic surfaces of implant components and tribo-films formed in the presence of proteins can both be disturbed by asperity contacts and wear debris. The total loss of material from metallic bearing components is clearly a combination of mechanical surface wear and tribo-corrosion, with indications that the latter can account for 0–40% of the total material loss.