Wear in Total Hip Prostheses: An Experimental Evaluation of Candidate Materials

Various investigators have attempted to evaluate the wear characteristics of different prosthetic materials in the laboratory.Duff- Barclay and Spillman (1966-67), described a hip joint simulator designed to test friction and wear in total joint prostheses.The simulator evaluated the performance of prostheses of various designs and materials under movement and pressure conditions similar to those pertaining to normal hip joints during walking.Tests were reported under dry conditions, in saline solution and in blood plasma.Titanium 160 and EN 58J stainless steel both exhibited high wear rates and were thought to be impractical in metal-to-metal prostheses.The lowest wear rate was elicited with a metalon-metal cobalt-chromium prosthesis, with a horseshoe-shaped acetabulum bearing.A decreased coefficient of friction was observed using plasma, and was attributed to the presence of metal-protein complexes on the metallic surface.Tests with a Delrin (polyacetal) acetabular component showed production of particles attributed to a surface-fatigue type of failure.With RCH 1000 no true signs of wear were evident in the acetabulum although a significant deformation of the acetabulum was seen.Charnley , in a discussion on bearing materials, called attention to the poor wear resistance of P.T.F.E.articulating against metal with 7 to 10 mm of wear in the plastic within a 2 1 / 2 year period.He found that for a 41 mm head, linear wear was 3 mm; for a 22 mm head, linear wear was 10 mm.The volume of wear particles was lower with the smaller head than with the large one.Trials with filled P.T.F.E.appeared to be satisfactory in the laboratory but not in the human.Laboratory tests showed that high molecular weight polyethylene had resistance to wear superior to P.T.F.E. by a factor of 500, although in vivo measurements indicated only a factor of 16.5 (Charnley 1970).Walker, Dowson, Longfield and Wright (1966-67), performed studies of friction and wear of artificial joint materials using a pin-on-disc machine.The specimens were tested both dry and lubricated with synovial fluid.Constant sliding speed and a nominal contact pressure of 19.6 x 10 6 nt/rn?were used.The disc was made from EN 58J stainless steel and the pins