SONICATION BRUSHING EFFECTIVELY REMOVES GRAM-NEGATIVE BIOFILM FROM TIBIAL BASEPLATES: AN IN VITRO STUDY

Aim Debridement, antibiotics and implant retention (DAIR) is the treatment of choice in acute periprosthetic joint infection (PJI), and residual biofilm on the retained components is likely after debridement. Chemical debridement has been studied rigorously, mechanical methods far less. Dental literature indicates that sonication brushing removes biofilm effectively, but its role in PJI remains largely unexplored. Gram-negative organisms cause 10 to 20% of PJI, E. coli being the most common among them, and they are isolated most often within the first year after arthroplasty, the window in which DAIR is used. DAIR performs worse in gram-negative infection. The purpose of this study was to determine whether sonication brushing removes E. coli biofilm from a tibial baseplate, alone and combined with pulsatile lavage. Methods Five size-D Ti-6Al-4V tibial baseplates were inoculated with E. coli (ATCC 25922) in lysogeny broth and incubated at 37 °C for 72 hours under static conditions. Treatment episodes were allocated to four groups: untreated control (n = 12), high-speed pulsatile lavage (n = 8), sonication brushing (n = 8), or sonication brushing followed by pulsatile lavage (n = 8). Baseplates were reused across runs and rotated between conditions. The primary outcome was viable bacteria (CFU/mL) recovered by bath sonication and serial dilution plating. The secondary outcome was residual biomass by crystal violet staining. CFU data were compared by one-way ANOVA on log10-transformed values with post-hoc Tukey correction. Crystal violet results are descriptive. Results Untreated baseplates yielded a mean of 2.48 × 106 CFU/mL. Pulsatile lavage alone reduced viable bacteria by 32.7% (1.67 × 106 CFU/mL; p = 0.40 vs. control). Sonication brushing achieved an 80.3% reduction (4.90 × 105 CFU/mL; p < 0.001), and the combination a 99.4% reduction (1.48 × 104 CFU/mL; p < 0.001). Every treated baseplate still yielded culturable bacteria. Crystal violet absorbance fell stepwise across treatment groups (30.8%, 36.1%, 44.5%), proportionally less than viable counts. Conclusions Sonication brushing effectively removed E. coli biofilm from titanium tibial baseplates, where pulsatile lavage alone did not. Combining brushing with lavage reduced the bacterial load the most. Viable bacteria remained after every treatment, so chemical decontamination of the retained implant stays important alongside mechanical debridement.