Sonication of orthopaedic implants: Impact of implant size, container dimensions, and sonication time on bacterial recovery.

BACKGROUND

Sonication aids diagnosis of implant-associated infections by detaching bacteria colonizing orthopaedic devices. Variations in implant size, container material, fluid volume, and sonication parameters may influence bacterial detachment and culture yield, potentially affecting interpretation of diagnostic thresholds. This in vitro study evaluated how implant size and sonication container characteristics influence recovery of Staphylococcus aureus from titanium implants.

METHODS

Titanium 7-hole locking compression plates (LCP; 577.8 mm2) and 3-hole titanium tibial plateau leveling osteotomy plates (TPLO; 2224.47 mm2) were exposed to S. aureus MU 12 for 30 min. Implants were sonicated in small, medium, and large plastic and glass containers for 1, 2, 5, or 10 min using a BactoSonic bath (40 kHz, 0.1 W/cm2). Sonication volume was either fixed or adjusted for complete implant submersion. Bacterial recovery was quantified as CFU/mL and analysed using t-test or ANOVA (P < 0.05).

RESULTS

The larger TPLO plates yielded significantly higher bacterial loads than LCP plates (P < 0.001). Glass containers resulted in higher recovery than plastic (P = 0.0146). Prolonged sonication significantly increased bacterial recovery at higher inoculum (P < 0.01). Container size generally did not impact recovery; however, for the smaller implant, the smaller container had significantly lower CFU than the medium-sized container (P = 0.0096). This effect was lost when the fluid volume was adjusted relative to implant size.

CONCLUSIONS

Implant size, container material, and duration significantly influence bacterial recovery, whereas container size appears less relevant. Without standardised sonication workflows, fixed CFU-based cut-offs for fracture related infection may be unreliable.