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Ref.: MmeBi14-001

Comparison of the fretting corrosion current of two commercial modular hip implants subjected to different levels of mechanical loading and cycling frequency

Apresentador: Sheyla Santana Carvalho

Autores (Instituição): Dos Santos, C.T.(Instituto Nacional de Tecnologia); Carvalho, S.S.(Instituto Nacional de Tecnologia); Cavalleiro, M.d.(Universidade Federal Fluminense); Monteiro, A.d.(Universidade Federal Fluminense); dos Santos, V.O.(Universidade Federal do Rio de Janeiro); Fernandes, W.G.(Instituto Nacional de Tecnologia);

Resumo:
Fretting corrosion in total hip arthroplasty (THA) implants seriously affects the in-service performance of these medical devices. Metal ions released due to corrosion can cause adverse tissue reactions, compromising patients' quality of life, and requiring implant replacement, which increases the risk of death. In this context, the release of ions is being considered one of the main causes of post-operative THA failure. The aim of this study is to compare two commercial modular hip implants subjected to accelerated fretting corrosion testing under different loading conditions and cycling frequency. Two groups of hip implants were evaluated: group I - CoCr/HNSS, composed of CoCr head (ASTM F1537) and HNSS stem (ASTM F1586); group II - SS/HNSS, composed of SS head (ASTM F138) and HNSS stem. The effect of two parameters (loading and frequency) on the fretting corrosion current of implants (specifically in the contact region between the head and the stem) was studied. Design of Experiments (DoE) allowed reducing the number of tests (fretting corrosion) required to 7 per group (including the 3 central points that made it possible to estimate the experimental error), which were carried out at loads 800, 2200, 3600N (using R=0.1) and at cycling frequencies of 1, 2 and 3 Hz. The fretting corrosion current was determined based on subtracting the total current from the resting current. The results showed that, at a low loading level (800 N), the fretting corrosion current was equal to 0 µA, regardless of the frequency adopted for the two groups. When increasing the load to 3600 N at 1 Hz, there was an increase in the fretting corrosion current to 0.9 and 4.6 µA for the SS/HNSS and CoCr/HNSS groups, respectively. When increasing the frequency from 1 to 3 Hz, for both groups of implants, the fretting corrosion current practically triples (2.8 µA) for the SS/HNSS group, and doubles (9.3 µA) for the CoCr/HNSS group. The measured currents were higher for the CoCr/HNSS group, composed of dissimilar materials between the head (CoCr) and stem (HNSS). Considering that hardness and corrosion resistance is higher for CoCr implants followed by HNSS and lower for SS implants, a lower fretting corrosion current was expected for pairs composed of CoCr/HNSS (more noble materials). However, it is possible that the use of dissimilar materials increased fretting corrosion by adding a galvanic pair effect. Furthermore, a greater fretting corrosion current is an indication that a greater release of ions and/or metallic particles has occurred. The greater release of these ions increases the potential to trigger an adverse tissue reaction, mainly due to the release of Co, Cr and Mo ions. These results highlight the need to avoid combining modular implants composed of dissimilar metallic materials.