UNASSIGNED: PURPOSE OF THE STUDY The wear of articular surfaces is considered one of the most important factors limiting the life of @entity572 ( @entity572 ). It is assumed that the particles released from the surface of a softer material induce a complex inflammatory response, which will eventually result in osteolysis and @entity1349 . Implant wear is related to a friction coefficient which depends on combination of the materials used, roughness of the articulating surfaces, internal clearance, and dimensions of the prosthesis. MATERIAL AND METHODS The selected parameters of the bearing couples tested were studied using an experimental device based on the principle of a pendulum. Bovine serum was used as a lubricant and the load corresponded to a @entity1 body mass of 75 kg. The friction coefficient was derived from a curve of slowdown of pendulum oscillations. Roughness was measured with a device working on the principle of interferometry. Clearance was assessed by measuring diameters of the acetabular and femoral heads with a 3D optical scanner. The specimens tested included unused metal-on-highly cross-linked @entity691 , ceramicon-highly cross-linked @entity691 and ceramic-on-ceramic bearing couples with the diameters of 28 mm and 36 mm. For each measured parameter, an arithmetic mean was calculated from 10 measurements. RESULTS 1) The roughness of @entity691 surfaces was higher by about one order of magnitude than the roughness of metal and ceramic components. The Protasul metal head had the least rough surface (0.003  m). 2) The ceramic-on-ceramic couples had the lowest clearance. Bearing couples with @entity691 acetabular liners had markedly higher clearances ranging from 150  m to 545  m. A clearance increased with large femoral heads (up to 4-fold in one of the couple tested). 3) The friction coefficient was related to the combination of materials; it was lowest in ceramic-on-ceramic surfaces (0.11 to 0.12) and then in ceramic-on- @entity691 implants (0.13 to 0.14). The friction coefficient is supposed to increase with a decreasing femoral head diameter. However, in the bearing couples with @entity691 liners manufactured by one company, paradoxically, the friction coefficient slightly increased with an increase in femoral head size from 28 mm to 36 mm. 4) The lowest friction moment (< 3.5 Nm) was found for ceramic-on-ceramic implants 28 mm in diameter; the highest values were recorded in metal-on- @entity691 bearing couples 36 mm in diameter (> 7 Nm). DISCUSSION Although our study confirmed that the bearing couples produced by different manufacturers varied to some extent in the parameters studied, in our opinion, this variability was not significant because it was not within an order of magnitude in any of the tests. CONCLUSIONS The study showed that both the friction coefficient and the friction moment are affected more by the combination of materials than by the diameter of a femoral head. The best results were achieved in ceramic-on-ceramic implants. Key words: @entity572 , bearing surfaces, wear, friction coefficient, friction moment, clearance.

[Determination of a Friction Coefficient for XXXX Bearing Couples].

@entity1 :: ('9606', 'Species') :: ['human'] @entity572 :: ('MESH:D006617', 'Disease') :: ['THA', 'total hip arthroplasty'] @entity691 :: ('MESH:D020959', 'Chemical') :: ['polyethylene'] @entity1349 :: ('MESH:D011475', 'Disease') :: ['aseptic loosening']
@entity572 :: (MESH:D006617,Disease) :: ['THA']
