Synopsis
The wear behavior of a femoral head made of zirconia (ZrO
2) against an acetabular cup made of ultrahigh-molecular-weight polyethylene (UHMWPE) was investigated using a hip joint simulator for five types of lubricants. Five types of lubricants were used: balanced salt solution (BSS), a BSS solution containing bovine serum albumin (A) and &ganma;-globulin (G) (BSS+A+G), and a BSS solution containing 1.5 times the concentrations of A and G (BSS+1.5(A+G)), as well as two types of bovine sera (CS1 and CS2). The effect of the total protein concentration in the lubricant on the wear rate was assessed. The weight loss of the UHMWPE cup was measured. Weight loss increased with the test duration for all lubricants except for BSS. The lubricant that produced the highest wear rate (mg/10
6 cycles) calculated from the weight loss during the test, was BSS+1.5(A+G), followed by BSS+A+G. Little weight change of the UHMWPE cup was observed for BSS. The wear rate increased with the concentration of protein, irrespective of the protein species. During the experimental observation period, the wear rate decreased in the order CS1 > BSS+1.5(A+G) > CS2 > BSS+A+G > BSS
~ 0. The comparison of quantitative measurements of individual particles in the lubricants showed that the morphology of each type of particle was dependent on the type of lubricant. Fibers and/or granules appeared in CS1 and CS2. In contrast, elongated fibers were mainly generated in BSS+A+G and BSS+1.5(A+G). These elongated particles formed by wear suggest that an adhesive mechanism, rather than the abrasive mechanism associated with asperities, was active. Our results suggest that the adhesive mechanism was active in lubricants containing proteins such as A and G.
Key words: hip joint, wear, hip simulator, lubricant, polyethylene debris
