The metal-on-metal (MoM) total hip prosthesis is widely used. However, the adverse reactions such as pseudotumor around the total hip prosthesis are observed. This is considered the effect of the corrosion of alloy which includes metal ion release and the wear particle generation. As materials for total hip prostheses, cobalt chromium (Co-Cr) alloy is used because of the wear resistance and corrosion resistance. The passive film on the surface of alloy contributes to corrosion resistance. The passive film is removed easily with friction. Therefore, metal ion is released from bare metal. However, this removal of passive film can be restored because of oxidation reaction with neighboring environment. The modular MoM total hip prosthesis such as acetabular component-femoral head or taper junction which connect femoral head and stem have friction interfaces. The friction amplitudes must be different among these interfaces. However, how sliding amplitude affects on removal of a passive film is unclear. The main purpose of this study was to investigate the effect of the sliding amplitude of the reciplocating micromotion on removal and reformation of the passive film of Co-Cr alloy. The behavior of the passive film was observed by measuring the electric potential of the alloy. Co-Cr alloy (ASTM F75) pin specimen and common tablet specimen were immersed in simulated body fluid PBS(−) and abraded with friction testing machine. The electronic potential between the pin and the Ag/AgCl reference electrode (RE-1C, ALS, Tokyo, Japan) were measured using a high impedance electrometer (HE-104E, HOKUTO DENKO, Tokyo, Japan). The friction amplitude was chosen from 0.2–2 mm. The reciprocating cycle was 1 Hz. The load of 10 N applied on the pin by a weight.Introduction
Methods
In these three years, many troubles have occurred in the arthroplasty by hip joint prostheses with metal on metal sliding surfaces. Anomalous reaction including a pseudotumor, which is supposed to be caused by the metal ions released from the implant surfaces, is the most serious problem for the patients1). This problem seriously confused us because there is the fact that ion release has not hardly occurred between a head and an acetabulum, where usual wear proceeds. The important clue was the stain that was sometimes found on the surfaces of the taper junction of retrieved prostheses. This stain has been generally estimated the evidence of the fretting corrosion. It has not been clarified why short range sliding enhances the corrosion, yet. In the present study, to elucidate this problem, we observed the behavior of the passive film of implant surfaces under the sliding conditions of fretting, which is presumed on the taper junction. In the present study, electric potential was measured as an indicator to assess the removal of the passive film of cobalt chromium (CoCr) alloy under the fretting conditions. A wear simulator (FPR-2100, RHESCA, Tokyo, Japan) was used for the testing apparatus with reciprocating motion. A Co-28Cr-6Mo alloy pin (Smith & Nepew, London, UK) specimen was 10 mm in diameter and abraded with the common material plate (Fig. 1). A load of 1 N was applied to a pin. The electronic potential between the pin and the Ag/AgCl reference electrode (HX-R5, HOKUTO DENKO, Tokyo, Japan) soaking in the PBS(−) as simulated biological fluid were measured using a high impedance electrometer (HE-104, HOKUTO DENKO, Tokyo, Japan) (Fig. 2). The sliding width was chosen 0.5–10 mm. The reciprocating cycle was chosen 0.5–2 Hz. The changes in the electronic potential of CoCr alloy were recorded during the sliding motion together with under the static conditions before and after the sliding motion.Introduction
Materials and Methods
