Multi-laboratory simulator studies on effects of serum proteins on PTFE cup wear

• Published in: Wear 2001-10, Vol.250 (1-12), p.188-198
• Main Authors: Clarke, Ian C., Chan, Frank W., Essner, Aaron, Good, Victoria, Kaddick, Christian, Lappalainen, Roejio, Laurent, Michel, McKellop, Harry, McGarry, William, Schroeder, David, Selenius, Mikko, Shen, Ming C., Ueno, Masuo, Wang, Aiguo, Yao, Jian
• Format: Article
• Language: English
• Subjects: Hip-prostheses; PTFE; Serum-proteins; Simulators; Wear
• ISSN: 0043-1648; 1873-2577
• DOI: 10.1016/S0043-1648(01)00656-1

A multi-laboratory, simulator study investigated the wear of polytetrafluorethylene (PTFE) cups run in bovine serum. Each laboratory used its own test protocol with a variety of simulator types. Our wear model incorporated 32mm dia CoCr heads matched to PTFE cups run with serum protein-concentrations in the range 17–69mg/ml. The multi-lab data demonstrated that protein-concentration had the most significant effect on wear performance. Both inverted and anatomical cups followed the same trend with first a rapid increase in wear-rates apparent for the initially low-protein levels and then a wear-rate reduction effect becoming apparent beyond 17mg/ml of proteins. The results showed that as the protein concentration increased from 17 to 69mg/ml, the magnitude of the wear-rates increased 200% but the protein wear-rate gradient decreased 24–60% with “inverted” and “anatomical” cups, respectively. This effect was more pronounced with ‘anatomical” than “inverted” cups. Thus, the wear-trends with “inverted” cups were generally the more consistent, particularly at the low-protein levels. Increasing the serum volume 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 consistent with the concept that low-concentrations of proteins promoted polymer wear but high-protein concentrations resulted in a protein-degradation phenomenon which progressively masked the actual polymer wear. In the selected protein range 17–69mg/l, the multi-laboratory simulator data consistently overestimated the average clinical wear-rate by at least 50–100% depending on protein range. It would, therefore, appear clinically relevant to study PTFE wear with an inverted-cup model using a large volume of serum but only in low-protein concentrations. The protein-related wear phenomena observed with PTFE cups in this multi-laboratory project may also have relevance for wear-simulation of UHMWPE cups.