Background and purpose: Commercial gentamicin-loaded bone cement beads (Septopal^®) constitute an effective delivery system for local antibiotic therapy. However, these beads are not commercially available in all parts of the world, and are too expensive for common use in others. Therefore, orthopedic surgeons worldwide make antibiotic-loaded beads themselves. However, these beads are usually not as effective as the commercial beads because of inadequate release kinetics. The aim of this study was to develop a simple, cheap and effective formulation to prepare gentamicin-loaded beads with release properties and antibacterial efficacy similar to the ones of commercially available beads.

Methods: Acrylic beads were first prepared with variable monomer contents: 500 μl/g polymer (100%), 375 μl/g polymer (75%), and 250 μl/g polymer (50%) to increase gentamicin release through the creation of a less dense polymer matrix. After optimal monomer content was defined, different gel-forming polymeric fillers were added to enhance the permeation of fluids into the beads. Polyvinylpyrrolidone (PVP) 17 was selected as a suitable filler, its concentration was varied and the antibiotic release and antibacterial efficacy of the final beads were compared with the ones of Septopal^® beads.

Results: Gentamicin release rate and extend of release from beads prepared with 50% monomer increased upon increasing the PVP 17 content in the beads. Beads with 15 w/w% PVP 17 released 87% of their antibiotic content within 336 h. Importantly, this is significantly more than the gentamicin-release from Septopal^® beads, that appeared confined to only 59% within 336 h. In addition, acrylic beads with 15 w/w% PVP 17 reduced bacterial growth up to 93%, which is a similar reduction as achieved with Septopal^®.

Interpretation: A simple, cheap and effective formulation and preparation process has been described for hand-made gentamicin-releasing acrylic beads, with release kinetics and antibacterial efficacy similar to the ones of commercially available Septopal^® beads.

Background and Purpose: The remarkably low wear of metal-on-metal (MOM) bearings involving cobalt-chromium (Co-Cr) alloys has led to a resurgence in its use. However, consequences of these wear particles and the corrosion products are for the most part unclear. Recent research efforts towards the bacteriological influences of the MOM-degradation products suggested that particulate MOM debris promotes planktonic bacterial growth. On the other hand, extremely high concentrations of metal ions, derived from salts, have shown to possess bacteriostatic effects (growth reduction) on planktonic growth and on biofilm formation. The effects of salt-derived metal ions were found to be inhibitory and not bactericidal (lethal to bacteria). However, these two findings were both found under static growth conditions and no studies have investigated these findings under more clinically resembling dynamic growth conditions. In addition, influences of Co-Cr particles on biofilm formation have not yet been studied. Therefore, the aim of this study was to evaluate how Co-Cr particles and Co-Cr ions affect biofilm formation under static and dynamic growth conditions.

Methods: A collection of clinically isolated bacterial strains were exposed to Co-Cr particles and Co-Cr ions in concentrations as found in serum and above as found in adjacent tissue. The experiments were conducted as well under static, as under dynamic growth conditions. Biofilm formation in wells, stained with live/dead viability staining and visualized by confocal laser scanning microscopy, was analyzed with COMSTAT, yielding biovolume, biofilm thickness, and live/dead ratio of the bacteria within the biofilm.

Results: Co-Cr particle concentrations of 20 g/L reduced biofilm formation significantly. Moreover, these particle concentrations were found to be bactericidal (killed the bacteria). The live/dead ratio decreased when culturing was done under dynamic growth conditions when compared to the static growth condition. Under both growth conditions, biofilm formation was inhibited at concentrations of 10/5 mg/L Co-Cr ions, as reported to occur in synovial fluids. Co-Cr ion concentrations up to 1/0,5 mg/L revealed no consistent influence on biofilm formation.

Interpretation: Long-term clinical data on infection rates for Co-Cr MOM-bearings are not yet available, but the current results suggest that Co-Cr ions may yield these prostheses less prone to biofilm formation and subsequent infection.

Clinical experience indicates the beneficial effects of antibiotic-loaded bone cement. Although in vitro studies have shown the formation of a biofilm on its surface they have not considered the gap between the cement and the bone. We have investigated bacterial survival in that gap. Samples with gaps 200 μm wide were made of different bone cements. These were stored dry (‘pre-elution’) or submersed in phosphate-buffered saline to simulate the initial release of gentamicin (‘post-elution’). The gaps were subsequently inoculated with bacteria, which had been isolated from infected orthopaedic prostheses and assessed for their sensitivity to gentamicin. Bacterial survival was measured 24 hours after inoculation. All the strains survived in plain cements. In the pre-elution gentamicin-loaded cements only the most gentamicin-resistant strain, CN5115, survived, but in post-elution samples more strains did so, depending on the cement tested. Although high concentrations of gentamicin were demonstrated in the gaps only the gentamicin-sensitive strains were killed. This could explain the increased prevalence of gentamicin-resistant infections which are seen clinically.