Gentamicin was described with negative effects on bone formation. Arginin-Glycin-Aspartat (RGD) sequences play a key role in the adhesion of osteoblasts and have proven to improve implant integration. We have already shown a significant reduction in infection rates by a combined gentamicin-hydroxyapatite (HA) and gentamicin-RGD-hydroxyapatite coating in a rabbit infection model for cementless joint prostheses.

The purpose of the study was to assess whether the gentamicin-HA coating had a negative effect on the implant integration and new bone formation, compared to pure HA coating, and whether this could be enhanced by additional gentamicin-RGD-HA coating.

There were 5 study groups (8 animals per group) with 5 different stainless steel K-wires: uncoated, HA coated, gentamicin-HA, RGD-coated, gentamicin-RGD-HA coated. A 2.0 mm K-wire with one type of coating was introduced into the intramedullary canal of the tibia. The tibiae were harvested after 12 weeks and standardised longitudinal and transverse sections were performed to study new bone formation around the implant and implant bone contact. New bone formation and osseointegration of the implant surface was assessed using histomorphometrical methods by computerised semi-quantitative analysis and histological methods.

There were no significant differences between the HA and the gentamicin-HA group although new bone formation and implant bone contact were always higher for the pure HA coating. Additional RGD coating on the gentamicin-RGD-HA coating did not show significant improvement of bone formation and implant integration compared to gentamicin-HA. There was a very similar histological appearance of new bone formation between all groups with very low frequency of giant cells, indicating good biocompatibility.

Gentamicin-HA coating did not have significant negative effects on bone formation and bone implant contact, compared to pure HA coating. In combination with the excellent ability to reduce infection rates, gentamicin-HA coating may have a high interest in cement-less arthroplasty.

Introduction: Similar local infection prophylaxis as in cemented total joint by antibiotic-loaded bone cement has not been possible yet for cementless prostheses. In this study, a gentamicin-coating which can be brought additionally onto standard hydroxyapatite (HA) coatings of cementless prostheses is presented. It was tested whether this gentamicin-coating can reduce infection rates in a rabbit infection model with Staphylococcus aureus compared to compared to standard-HA coating. Furthermore, the biocompatibility of this gentamicin coating was investigated.

Materials and Methods: Staphylococcus aureus with a dose of 10(7) CFUs was inoculated into the intramedullary canal of the tibia of 30 rabbits followed by the implantation of standard hydroxyapatite (HA) K-wires, K-wires coated with a HA--gentamicin combination, and K-wires coated with a HA-RGD-gentamicin combination, 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-pulse field gel electrophoresis were carried out to detect infection. Infection was defined as positive culture growth from the bone and/or cement samples. In another study with 40 rabbits biocompatibility of the two gentamicin-coating types was assessed after an implantation time of 12 weeks and compared to pure HA-coating and uncoated implants.

Results: Infection rates were 88% (7 of 8 animals) for the standard HA, 0% (0 of 9 animals) for the HA-gentamicin and 0% (0 of 10 animals) for the HA-RGD-gentamicin group. There was a statistically highly significant reduction of infection rates by both gentamicin-coating types compared to standard HA-coating (p < 0.001). The animals that were identified to have positive culture growth corresponded to the animals that showed clinical signs of infection. An excellent correlation between agar plating testing results of the K-wires and of the bone samples was found. Detailed histology showed cortical lysis, abcess and sequester formation in the infected animals. There were no major differences in the biocompatibility between the different groups. There were only a few giant cells and regions of bone marrow necrosis in the gentamicin-groups which was comparable to the control implants. There was a very similar histologic appearance of the gentamicin coatings and the standard HA coating.

Conclusion: Both gentamicin-coating types showed significant improvement of infection prophylaxis compared to standard HA coating. Furthermore, both gentamicin coating types revealed good biocompatibility after 12 weeks. Therefore, HA-gentamicin and HA-RGD-gentamicin coatings could help to reduce infection rates in cementless arthroplasty in all day clinical use