Lubricant composition is known to affect in vitro (simulator) wear of polymeric acetabular components. Clinical acetabular components, fabricated from both ultrahigh molecular weight polyethylene (UHMWPE) and polytetrafluoroethylene (PTFE), were tested against cobalt-chromium 32-mm ball heads, with the use of various lubricants, with different compositions and concentrations of bovine and calf serum as well as hyaluronic acid, in tests which lasted one million cycles. The type of proteins and their relative concentration in the lubricant affected the wear rate of both UHMWPE and PTFE. Increasing protein concentration reduced the UHMWPE wear rate but increased the PTFE wear rate. For a given total protein concentration, increasing the albumin/globulin (A/G) ratio led to a significant reduction in the wear rate for PTFE. A similar but smaller effect was found for UHMWPE. The relative wear-rate ratio between PTFE and UHMWPE depends on both the total protein concentration and the specific protein concentration (albumin/globulin ratio). The average clinical wear rates for both PTFE and UHMWPE and the average wear-rate ratios between them were reproduced when the serum lubricant contained total protein concentration and A/G ratio within normally observed physiological ranges. It is recommended that lubricants for simulator testing be standardized to control total protein content as well as albumin/ globulin ratio.

Cases of fretting and corrosion at the taper junction have been reported in large metal-on-metal bearing combinations, and more recently, this concern has included metal-on-polyethylene bearing combinations. Many of these patients have been revised due to adverse local tissue reaction secondary to taper corrosion. This taper corrosion-related adverse local tissue reaction seems to be a multifactorial issue and difficult to assess. The aim of this study was to look at one potential variable, the impaction behavior (impaction force, number of blows, etc.) of orthopedic surgeons, and understand how this can affect the locking strength of tapers. A group of experienced orthopedic surgeons were asked to use their typical surgical approach to impact a femoral head onto a hip femoral stem using an Operating Room (OR)-simulated test setup. Impaction parameters such as impaction force, velocity, and energy, as well as the number of impacts, were characterized and applied in a bench-top study used to evaluate the effect of these parameters on the initial stability of the taper junction. High variation was found in the surgical impaction parameters, but overall it was determined that increased impaction force correlated to superior stability of the taper junction.

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