Wear pattern on a retrieved Total Knee Replacement: The “fourth body abrasion”

Abstract

Released debris in a replaced knee, such as bone loose, bone cement debris and metallic particles, are responsible for a third body abrasion of the Polyethylene (PE) mobile bearing superior surface and therefore compromise the Total Knee Replacement (TKR) implant longevity. To analyze the upstream and the downstream mechanisms of such abrasion mode, a set of randomized topographical measurements of the PE surface was performed. A Monte Carlo simulation demonstrated two periods of bead loosening from the porous coating. The released coating beads are then entrapped in the articulating interface. The relative motion between the PE insert and the Cobalt-Chromium (CoCr) femoral component and the load transmitting through the knee drive the bead to roll and to generate large scratches (mean width of 200μm) in the PE matrix. Once embedded, the beads are abraded by the upper metallic surface, releasing metallic debris tending to spread on the entire PE surface. These CoCr particles act in the PE wear as the coating beads at a smaller scale, as suggested by a fine scratching pattern (mean width of 30μm) and PE debris agglomerate generation. As a result, these metallic debris are responsible for a PE “fourth body abrasion”.