IN-VIVO MECHANICAL AND HISTOLOGICAL CHARACTERISTICS OF HA-COATED IMPLANTS VARY WITH COATING VENDOR

The purpose of this study was to evaluate the interface attachment str ength and histology of hydroxylapatite (HA) coated and uncoated titani um and cobalt-chromium alloy implants. The canine transcortical plug m odel was utilized. Four different hydroxylapatite coatings were evalua ted. In vitro analysis confirmed that all coatings met FDA guidelines for HA coatings. An unspecified FDA parameter, porosity was found to r ange from 5-15%. Mechanical testing of the bone-implant interface demo nstrated large variation in the performance of the coatings. However, further evaluation of two of the coatings did not demonstrate variatio ns in mechanical characteristics. The histologic findings confirmed th e mechanical testing results. The coatings which demonstrated the best mechanical characteristics had excellent bone apposition and uniformi ty and maintenance of the HA coating at all time periods upon histolog ic evaluation. Conversely, the coatings which demonstrated inferior me chanical characteristics demonstrated variable amounts of bone apposit ion and moderate to severe coating degradation and breakup. Cell-media ted osteolysis was observed in regions of severe coating degradation, and particle migration was noted in regions far from the interface. It was hoped that the four coatings would behave similarly as they all m et current FDA guidelines. The only parameter which differed significa ntly among the coatings was coating porosity. Our results indicate tha t coatings with large porosities were associated with increased coatin g degradation and poor mechanical performance and osteolysis at the bo ne-coating interface. (C) 1995 John Wiley and Sons, Inc.