Abstract

The most important advantage of using modular hip joint endoprostheses is the possibility to adapt the endoprosthesis to the morphology and size of individual patients. However, the additional contact surface is subjected to fretting wear due to mutual micro displacements and the aggressive chemistry of the environment inside the human body (fretting corrosion). Today’s hip endoprostheses are generally composed of a hip stem, a femoral ball head and an acetabular cup (Figure 1). The hip stem is made of stainless steel, CoCrMo or a Ti alloys. The femoral ball head is made of stainless steel, CoCrMo, or a ceramic material. In the case of a modular hip stem, i.e. with a modular neck portion, the materials used are generally CoCrMo and Ti6Al 4V. (The interface between femoral ball head and the acetabular cup is an articulating surface and not the subject of this research project.) In this framework, a comparative study of the fretting corrosion resistance of the three most common metallic material combinations occurring in a modular, the non-articulating connection of total hip joint endoprostheses (CoCrMo-CoCrMo, CoCrMo-Ti6Al4V, and Ti6Al4V-Ti6Al4V) was undertaken. Studies were performed with a tribological tester, working in articulating-reciprocating motion, integrated with a potentiostat equipped with a tri-electrode system. The tribosystem consisted of a fixed stem pressed with a constant force to a plate performing the reciprocating motion of a predetermined frequency and amplitude. The tests were performed in diluted bovine serum at 37°C. Based on the obtained results, it was found that the greatest resistance to corrosion in static conditions was exhibited by the CoCrMo-CoCrMo friction pair, while the lowest ΔE value was obtained by CoCrMo-Ti6Al4V. It also confirmed the existence of a correlation between the intensity of the depassivation process caused by the mechanical destruction of the surface layer and the friction resistance values in the tribological system.

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