Biomaterial-associated infection of gentamicin-loaded PMMA beads in orthopaedic revision surgery.

In two-stage orthopaedic revision surgery, high local levels of antibiotics are achieved after removal of an infected prosthesis through temporary implantation of gentamicin-loaded beads. However, despite their antibiotic release, these beads act as a biomaterial surface to which bacteria preferentially adhere, grow and potentially develop antibiotic resistance. Gentamicin-loaded beads were retrieved from 20 patients with prosthesis-related infections. Excised tissue samples were taken for routine culture, while beads were analysed in an extensive laboratory procedure. Extensive culture procedures indicated the presence of bacteria on gentamicin-loaded beads in 18 of the 20 patients involved, while 12 of these 18 patients were considered free of infection by routine culture. Nineteen of 28 bacterial strains isolated were gentamicin resistant and cultures from three patients yielded highly gentamicin-resistant sub-populations. It is concluded that routine culture of excised tissues in orthopaedic revision surgery is inadequate to ascertain full eradication of infection, especially as infecting, antibiotic-resistant bacteria preferentially adhere to and grow on gentamicin-loaded beads. Extensive examination of the bead surfaces is proposed as a more reliable indication that infection has been eradicated.