Effects of hydroxyapatite coating on Ti-6Al-4V implant-site infection in arabbit tibial model

To investigate the effect of implant type after direct contamination, a hyd roxyapatite-coated or noncoated Ti-6A1-4V implant was inserted into both ti biae of 32 New Zealand White rabbits. Prior to implantation, the left tibia was contaminated with increasing concentrations of Staphylococcus aureus ( 10(2)-10(5) colony-forming units), ranging from very low (10(2)) to relativ ely high (10(5)). Four weeks after implantation, half of the tibial bone ad jacent to the implant was harvested for bacteriological examination. Bacter ial counts were quantified by plating serial dilutions. For the histologica l evaluation, sections of the implant with the remaining tibia were examine d by semiquantitative scoring of infection parameters. The bacteriological data showed the inoculum dose and implant type to have a significant effect on the culture outcome: more bacteria were retrieved from the hydroxyapati te-coated implants than from the noncoated titanium implants. Histological evaluation showed an increased score for the infected left tibiae compared with their contralateral control. In addition, with increasing inoculum dos age, the difference between the two types of implant increased. We demonstr ated that infections can occur with biocompatible, noncemented implants and that they are related to the dose of the original inoculum. Bacteria were more likely to grow onto or next to the hydroxyapatite implants than on tit anium implants and resulted in a more severe histopathological characteriza tion of infection.