Abstract
Aseptic loosening due to particle disease is one of the major problems for THA. Since simulator studies are expensive, there is a need for screening tests to evaluate different pairings. Recent publications have shown that multiaxial motions are important in reproducing appropriate wear behaviour. The objective of the study was to design a simple bidirectional pin-on-disc screening test with multidirectional motions allowing on-line dimensional wear measurements and to compare the measured in-vitro wear rate with the observed in-vivo wear rate.
The multidirectional motions were obtained by a rotating pin on a rotating disc. With one disc rotation, the pin rotates 4 times, which leads to 4 changes in the wear direction. The wear characteristics were: load 3.45 MPa, lubricant 33% calf serum – 67% Ringer’s solution, temperature 37°C. The wear rate was measured on-line by the dimensional change in the height of the pin and by the conventional gravimetric method.
Following results were obtained: Wear Coefficient [mm3/Nm]: 1.446 10-6 ± 0.447 10-6 [CoCrMo – UHMWPE] – 0.515 10-6 ± 0.136 10-6 [Al2O3- UHMWPE] /Linear Wear Rate [mm/106 cycles]: 0.132 ± 0.041 [CoCrMo – UHMWPE] – 0.047 ± 0.012 [Al2O3- UHMWPE] /Gravimetric Wear Rate [mg/106 cycles]: 2.104 ± 0.709 [CoCrMo – UHMWPE] – 0.769 ± 0.205 [Al2O3- UHMWPE].
This bi-directional screening test with shear motions has the following characteristics: Gives the three wear parameters /Shows s significant difference between the CoCrMo – UHMWPE and the Al203 – UHMWPE pairing /Demonstrates a relatively good agreement between the in-vivo and the in-vitro measurements.
This type of screening tests will provide some earlier information concerning the tribological behaviour of pairing for total hip joints.
