A multi-laboratory, simulator study investigated the wear of polytetrafluor
ethylene (PTFE) cups run in bovine serum. Each laboratory used its own test
protocol with a variety of simulator types. Our wear model incorporated 32
mm dia CoCr heads matched to PTFE cups run with serum protein-concentratio
ns in the range 17-69 mg/ml. The multi-lab data demonstrated that protein-c
oncentration had the most significant effect on wear performance. Both inve
rted and anatomical cups followed the same trend with first a rapid increas
e in wear-rates apparent for the initially low-protein levels and then a we
ar-rate reduction effect becoming apparent beyond 17 mg/ml of proteins. The
results showed that as the protein concentration increased from 17 to 69 m
g/ml, the magnitude of the wear-rates increased 200% but the protein wear-r
ate gradient decreased 24-60% with "inverted" and "anatomical" cups, respec
tively. This effect was more pronounced with "anatomical" than "inverted" c
ups. Thus, the wear-trends with "inverted" cups were generally the more con
sistent, particularly at the low-protein levels. Increasing the serum volum
e by two-fold in one study increased the PTFE wear-magnitudes approximately
40% and the protein-wear gradient by 30%. These PTFE wear phenomena were c
onsistent with the concept that low-concentrations of proteins promoted pol
ymer wear but high-protein concentrations resulted in a protein-degradation
phenomenon which progressively masked the actual polymer wear. In the sele
cted protein range 17-69 mg/l, the multi-laboratory simulator data consiste
ntly overestimated the average clinical wear-rate by at least 50-100% depen
ding on protein range. It would, therefore, appear clinically relevant to s
tudy PTFE wear with an inverted-cup model using a large volume of serum but
only in low-protein concentrations. The protein-related wear phenomena obs
erved with PTFE cups in this multi-laboratory project may also have relevan
ce for wear-simulation of UHMWPE cups. (C) 2001 Elsevier Science B.V. All r
ights reserved.