Osteoarthritic Human Synovial Fluid Alters CoCrMo Electrochemical Properties on a Patient-Specific Basis

Cobalt-chromium-molybdenum (CoCrMo) femoral components are widely used in total knee arthroplasty (TKA). However, recent retrospective clinical trials associate moderate adverse local tissue reactions with CoCrMo release in the knee. Additionally, gaps persist in our understanding of the fundamental corrosion processes that occur at the CoCrMo-synovial fluid interface. In this study, we investigated the electrochemical behavior of CoCrMo in human synovial fluid obtained at the time of primary TKA, using CoCrMo in phosphate-buffered saline (PBS) as a comparison. Synovial fluid was collected from 118 patients immediately before arthroplasty, then transferred to a three-electrode electrochemical cell with a wrought CoCrMo alloy working electrode. To quantify electrochemical properties, open circuit potential (OCP), electrochemical impedance spectroscopy, and linear polarization tests were run. Generally, the properties varied on a patient-by-patient basis and significantly differed (p < 0.05) from comparison tests performed in PBS. In human synovial fluid, we measured OCPs between a range of -0.38 and 0.15 V and corrosion potentials (E_corr) between -0.95 and -0.2 V. Additionally, we reported instantaneous corrosion rates (1/R_p) spanning nearly four orders of magnitude. The variability we documented suggested that the electrochemical properties of CoCrMo implants may depend on the patient's local physiological environment, influenced by the biological and chemical components of synovial fluid. Statement of Clinical Significance: This study shows that human synovial fluid affects the electrochemical behavior of CoCrMo, evidenced by the variation on a patient-by-patient basis. This study may have implications for long-term biological response to orthopaedic implants, including total knee arthroplasty.