The origin of submicron polyethylene wear debris in total hip arthroplasty

The microscopic morphology of worn polyethylene surfaces was compared with that of the associated polyethylene particles for acetabular cups tested in a wear simulator and for cups worn in vivo, using scanning electron microscopy. In the absence of significant third-body abrasive damage, the articulation of the ball in the cup produced a visually polished surface on the polyethylene. On a micron scale, the morphology of the worn polyethylene from in vitro and in vivo wear included nodules and fibrils consistent with adhesive, abrasive, and microfatigue wear mechanisms. Larger wear features, such as deep scratches or pits measuring in 10s of microns, that were seen in the in vivo cups were attributed to third-body wear. The polyethylene particles isolated from the serum lubricants of the wear tests and from the periprosthetic tissues were primarily submicron in size, were either rounded or elongated, and were consistent with the submicron wear features seen on the cup surfaces. It is the submicron particles that are associated with inflammatory periprosthetic bone loss in total hip replacement. Although the mean dimensions of the particles generated in vitro were slightly smaller than those of the in vivo particles, the overall morphologies were very comparable, suggesting that the same lubrication and wear processes were acting in the simulator as in vivo.