Effects of gentamicin and gentamicin-RGD coatings on bone ingrowth and biocompatibility of cementless joint prostheses: an experimental study in rabbits.

Antimicrobial coatings are of interest as a means to improve infection prophylaxis in cementless joint arthroplasty. However, those coatings must not interfere with the essential bony integration of the implants. Gentamicin-hydroxyapatite (gentamicin-HA) and gentamicin-RGD (arginine-glycine-aspartate)-HA coatings have recently been shown to significantly reduce infection rates in a rabbit infection prophylaxis model. The purpose of the current study was to investigate the in vitro elution kinetics and in vivo effects of gentamicin-HA and gentamicin-RGD-HA coatings on new bone formation, implant integration and biocompatibility in a rabbit model. In vitro elution testing showed that 95% and 99% of the gentamicin was released after 12 and 24 h, respectively. The in vivo study comprised 45 rabbits in total, with six animals for each of the gentamicin-HA, gentamicin-RGD-HA group and control pure HA coating groups for the 4 week time period, and nine animals for each of the three groups for the 12 week observation period. A 2.0 mm steel K-wire with one of the coatings under test was placed in the intramedullary canal of the tibia. After 4 and 12 weeks the tibiae were harvested and three different areas (proximal metaphysis, shaft area, distal metaphysis) were assessed by quantitative and qualitative histology for new bone formation, direct implant-bone contact and the formation of multinucleated giant cells. The results exhibited high standard deviations in all subgroups. There was a trend towards better bone formation and better direct implant contact in the pure HA coating group compared with both gentamicin coatings after 4 and 12 weeks, which was, however, not statistically significant. The number of multinucleated giant cells did not differ significantly between the three groups at both time points. In summary, both gentamicin coatings with 99% release of gentamicin within 24 h revealed good biocompatibility and bony integration, which was not statistically significant different compared with pure HA coating. Limitations of the study are the high standard deviation of the results and the limited number of animals per time point.