CoCrMo metal release in metal-on-highly crosslinked polyethylene hip implants

Increasing cases of adverse local tissue reactions (ALTRs) associated with metal release have been observed in patients with metal-on-highly crosslinked polyethylene (MoP) hip implants, the most common design in total hip replacements. Studies have demonstrated the metal release from fretting corrosion at the head-neck junction, but rarely investigated tribocorrosion associated metal release at articulating surfaces in MoP hip implants. The objective of this study is to investigate both tribocorrosion at the articulating surfaces and fretting corrosion at the head-neck junction in CoCrMo femoral heads, as well as their association with metal species released in periprosthetic tissues and body fluids in MoP hip systems. Twenty-three patients with ALTRs associated with MoP implants were included. Systematic analyses were performed on the wear damage in articulation, corrosion at the head-neck junction and their correlation with degradation products observed in synovial fluid, periprosthetic tissues, and serum. Results showed that tribocorrosion at the articulating surfaces contributed to the elevated concentration of both Co and Cr ions in serum, while fretting corrosion at the head-neck junction mainly released Co ions to serum. Both tribocorrosion at the articulating surfaces and fretting corrosion at the head-neck junction released particles rich in chromium and phosphate, the dominant particles found in synovial fluids and tissues. This study provides strong evidence that tribocorrosion at the articulating surfaces in MoP hip implants could result in significant metal release. This information should be taken into account when studying the mechanisms of ALTRs and developing strategies of preventing metal release in total hip replacements.