Do current wear particle isolation procedures underestimate the number of particles generated by prosthetic bearing components?

Hip simulator serum samples containing ultra-high molecular weight polyethy lene (UHMWPE) wear debris were digested in acid, and replicate digests were filtered through either a 0.2 or a 0.05 mum pore size membrane. The recove red particles were characterized using Fourier transform-infrared spectrosc opy (FT-IR) and scanning electron microscopy (SEM). Debris deposited on bot h the 0.2 and 0.05 mum membranes were identified as UHMWPE by FT-IR and wer e predominantly submicron and round, with occasional elongated fibrils. The mean and median diameters of the particles on the 0.05 mum membranes were significantly lower than those of the particles on the 0.2 mum membranes. O ver half of the particles on the 0.2 mum membranes had diameters which were below the specified pore size, whereas only a small percentage (2.8%) of p articles on the 0.05 mum membranes were smaller than the specified pore siz e. More than twice as many particles were recovered on the 0.05 mum membran es than the 0.2 mum membranes. These findings indicate that a substantial n umber of wear particles passed freely through the pores of the 0.2 mum memb ranes, which resulted in an underestimation of particle number and an overe stimation of particle size. Because the cellular response to wear debris ha s been found to be dependent upon particle number and size, among other fac tors, the introduction of a new orthopaedic bearing material should be supp orted by an accurate description of wear particle parameters. To ensure an accurate description of particle characteristics, it is recommended that fi lter membranes with very fine pore sizes (at most 0.05 mum) be used to isol ate UHMWPE wear debris from joint simulator serum and periprosthetic tissue . (C) 2001 Elsevier Science B.V. All rights reserved.