Electrochemical and Corrosion Behavior of a Retrieved Cobalt–Chromium Knee Prosthesis After Two Years of In Vivo Exposure

Current studies on retrieved implants indicate that the cobalt–chromium (CoCr) femoral component undergoes surface degradation in vivo due to the combined action of cyclic mechanical loading, sliding contact, and the aggressive physiological environment. The synergistic interaction between wear and corrosion processes can compromise the integrity of the passive oxide layer, promoting material degradation, metallic ion release, and ultimately contributing to implant failure and revision surgery. Understanding the electrochemical response of worn implant surfaces is therefore essential for improving the long-term performance of knee prostheses.

In this study, a retrieved CoCr femoral component explanted after two years of clinical service was investigated to evaluate the influence of in vivo wear on its corrosion behavior. Two representative regions were identified: a worn area located on the medial condyle and a non-worn area on the anterior surface of the prosthesis. Since the wear scars were macroscopically visible, surface characterization was performed using stereomicroscopy to document the extent and morphology of the damage.

Electrochemical characterization was conducted in phosphate-buffered saline (PBS, pH 7.4) at 37 °C to simulate physiological conditions. A custom electrochemical cell holder was fabricated by 3D printing to isolate and evaluate each selected region independently. The corrosion behavior of both zones was assessed through open circuit potential, electrochemical impedance spectroscopy, linear polarization resistance, and potentiodynamic polarization measurements.

The results provide information on the effect of in vivo wear-induced surface degradation on the passive behavior and corrosion resistance of CoCr knee implants. Differences in electrochemical response between worn and non-worn regions are discussed in terms of passive film stability and surface damage, contributing to a better understanding of tribocorrosion mechanisms in retrieved orthopedic prostheses.