Combating orthopaedic implant infections with therapeutic ultrasound and shockwaves

Orthopaedic implant infections caused by biofilm-forming bacteria pose significant clinical and economic challenges due to high revision rates and increasing antibiotic resistance. Biofilms limit antibiotic penetration, rendering many conventional treatments ineffective. Cavitation, either spontaneous or facilitated by cavitation nuclei, can mechanically disrupt biofilms, offering a promising alternative. This study evaluates the efficacy of therapeutic ultrasound (US) and shockwaves (SW) in treating Staphylococcus aureus biofilms on clinically relevant implant materials, both independently and combined with antibiotics. In vitro biofilms were cultured on stainless steel, hydroxyapatite, and titanium discs (10–12 mm). Treatments included scanning US (0.95 MHz, 2.5 MPa PNP, 500 Hz pulse repetition frequency, 10% duty cycle, 10 s per location across nine positions) with in-house protein-based cavitation nuclei and SW (3.5 MPa PNP, 0.5 Hz PRF, 50 pulses). Passive cavitation detection monitored emissions during treatment. Biofilm disruption was quantified by fluorescence imaging and bacterial colony-forming unit counts. Both US and SW significantly reduced biofilm burden, with substrate-specific effects and distinct spatial disruption patterns (US: 1.5±0.8 and SW: 4.0±1.1 log reduction). Ongoing work is assessing whether detached aggregates exhibit increased antibiotic susceptibility. These findings support cavitation-based methods as minimally invasive adjuncts to enhance antibiotic efficacy and reduce revision surgeries.