Shape design of sliding surfaces of hip joint prostheses, the trial manufacture and the evaluation of lubricating ability

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Fluid film formation is necessary for long term reliability of a total hip prosthesis because solid contact of the prosthesis induces serious wear. Radial clearance is an important factor. Which radial clearance is appropriate should be clarified. We prepared some specimens with high accuracy of polishing, which were balls and cups of the Co-Cr-Mo alloy with a common radius of 16 mm and several radial clearances. Their lubricating ability was evaluated by a friction test using a pendulum machine under the load of 600 N. As the results, the frictional coefficient was the minimum where the radial clearance was 20-30 micro meter. The lowest value of frictional coefficient was, however, measured over 0.1. This results showed that the lubricating ability is unfortunately insufficient under the appropriate conditions of the metal on metal articulation.