INTRODUCTION

Surgical site infections (SSI) in orthopaedics are a major source of postoperative morbidity. Although perioperative antibiotic prophylaxis is a common practice, orthopaedic infections are still high in numbers, due to the increasing use of osteosynthesis material and implants. Implants are avascular and can be easily colonized with biofilm-producing germs. For both, effective prophylaxis and treatment of orthopaedic infections, the right choice of the antibiotics used, the mode of application (only systemic or systemic & local), the timing, dosage and the duration of antibiotics are of extremely high importance. Their inappropriate use does not only lead to failures in prevention or treatment of infections, but may also promote microbial resistance development and may cause serious side effects for the patients.

Infections in total joint arthroplasty, particularly with multiresistant bacteria, are a serious problem. A new nanoparticulate silver cement had previously shown good biocompatibility combined with good in vitro antimicrobial activity against multiresistant bacteria.

The purpose of the current study was to evaluate the antibacterial activity of nanoparticulate silver cement against biofilm-building methicillin-resistant S. aureus (MRSA) in a rabbit model and to compare it to that of gentamicin-loaded cement.

Gentamicin cement or nanoparticulate silver bone cement was injected into the proximal half of one femur in 10 animals, respectively. Before hardening of the cement 10⁷ or 10⁸ colony forming units of MRSA with high gentamicin resistance were inoculated at the cement bone interface in 5 rabbits of each group. The animals were euthanized after 14 days and both the cement adjacent bone and the cement itself were studied using microbiological and histological methods. Infection was defined as positive culture growth from the bone and/or cement samples.

Infections rates were 100% for the gentamicin group (10 of 10 animals had infection) and 30% for the NanoSilver group (3 of 10 animals). Thus, nanoparticulate silver bone cement significantly reduced infection rates by 70%.

Nanoparticulate silver cement exhibited good antimicrobial activity in the prophylaxis of cement-related infections with MRSA and is therefore a promising alternative in total joint arthroplasty.

Introduction: Deep periprosthetic infections are infrequent but devastating situations in total joint arthroplasty. During the last years the total number and the percentage of total joint infections with multiresistant bacteria has increased. The aim of this study was to investigate the antimicrobial activity of a new bone cement loaded with nanoparticulate silver against bacteria with different antibiotic resistance.

Material and Methods: An in vitro proliferation test was used to test antimicrobial properties of 1% nanoparticulate silver bone cement, gentamicin-loaded, tobramycin-loaded and plain bone cement. This in vitro testing method consisted of two incubation steps. During the first step the tested bacteria could adhere to the bone cement surface. In the second step bacteria either seeded out of vital daughter cells in case of no antimicrobial effect of the cement or were killed by the antibacterial properties of the cement. Seeding out of daughter cells was detected by a microplate reading system resulting in specific time proliferation curves. Several staphylococci and gram-negative strains with different resistance profiles against methicillin, tobramycin, and gentamicin were tested including MRSA and MRSE.

Results: 1% nanoparticulate silver bone cement showed bactericidal effect against all tested strains, including MRSA and MRSE. Gentamicin and tobramycin cement was not effective against bacteria with high resistance level against the respective antibiotic. Plain bone cement was not effective against any strain.

Conclusion: 1% nanoparticulate silver bone cement exhibited excellent antibacterial properties that could not be reached by gentamicin or tobramycin-loaded cement. Good activity against MRSA could also already be shown in a first animal trial. If further in vivo investigations confirm these promising results nanoparticulate silver bone cement is a new alternative for prophylaxis in total joint arthroplasty.