The effects of combined gentamicin–hydroxyapatite coating for cementless joint prostheses on the reduction of infection rates in a rabbit infection prophylaxis model

Infections remain a critical issue in total joint arthroplasty. Addition of antibiotics to bone cement was shown to significantly improve antimicrobial prophylaxis in cemented joint arthroplasty. In cementless joint arthroplasty a comparable prophylaxis by local antibiotics has not been possible yet. The aim of the current study was to investigate the antimicrobial effect of two different gentamicin–hydroxyapatite (HA) coatings for cementless prostheses in a rabbit infection model. Staphylococcus aureus with a dose of 107 CFUs was inoculated into the intramedullary canal of the tibia of 30 rabbits followed by the implantation of standard steel HA K-wires (n=10), steel K-wires coated with a gentamicin–HA combination (n=10), and steel K-wires coated with a gentamicin–RGD–HA combination (n=10), respectively. The animals were sacrificed after 28 days and clinical, histological and microbiological assessment on the bone and on the removed K-wire itself by agar plating and DNA-pulsed field gel electrophoresis were carried out to detect infection. There was a statistically significant reduction of infection rates by both gentamicin-coating types (0 infections in both groups) compared to standard HA coating (7 infections in 8 animals; 2 animals were lost due to acute diarrhea) (p<0.001). An excellent correlation between agar plating testing results of the K-wires and of the bone samples was found. Detailed histology showed cortical lysis, abscess and sequester formation in the infected animals. Both gentamicin-coating types showed significant improvement of infection prophylaxis compared to standard HA coating and, therefore, this coating technology could help to improve infection prophylaxis in cementless total joint arthroplasty. In further studies biocompatibility of the coatings has to be assessed.