Bacterial attachment and initial biofilm formation on the metal tibial tray and plastic spacer interfacing surfaces of total knee components: An in vitro scanning electron microscopy study.

Abstract

Periprosthetic joint infection (PJI) is a challenging complication of total knee arthroplasty (TKA). Bacterial biofilm formation is strongly implicated in PJIs, and renders the bacteria tolerant of antibiotic therapy and innate immunity. However, there is little information on where biofilms may reside in the reconstructed joint. In previous mapping projects using an agar overlay 'implant surface culture' (ISC) method we found evidence that biofilm was forming in the gap between the polyethylene spacer and the tibial tray components explanted from TKA patients undergoing revision for PJI. We hypothesized that bacteria could enter this gap and attach to form biofilms on both plastic and metal interfacing surfaces. We inoculated spacers and tibial tray components recovered from PJI patients that had been cleaned and reassembled with Staphylococcus epidermidis. We used scanning electron microscopy (SEM) to image the surfaces after an incubation of 3 days with daily media changes and analyzed the surface concentration of bacteria on flat surfaces and associated with surface features (slots, screw holes, ridges). Examination and quantification at multiple magnifications revealed a range from a sparse covering of bacteria on the flat areas to more extensive biofilms in monolayers and small aggregates around and within features in the tray. The polythene surfaces had three times more bacteria than the metal (P < 0.05). In the four features measured there were six times more bacteria that were associated with adjacent flat surfaces, but this was not statistically significant (P > 0.05). Bacteria can attach and initiate biofilm formation in the metal-polyethylene gap on both surfaces and are most concentrated in association with surface features. The gap may provide a niche where biofilm could reside with protection from antibiotics as well as phagocytic cells and other components of host immunity, and even irrigation and debridement procedures in a partial exchange.