S. Adam Hacking - Dept. of Biomedical Eng., McGill University

Also Appearing at the Hip Society: Feb 16 1:00 p.m for the:

The Otto Aufranc Award:

The Relative Contributions of Surface Chemistry and Topography To the Osseointegration of HA Coated Implants

S.A. Hacking, M. Tanzer, E.J. Harvey, J.J. Krygier and J.D. Bobyn

The positive effect of HA coatings on osseointegration has been attributed to its chemistry and its ability to increase the concentration of calcium and phosphate in the microenvironment, immediately adjacent to the implant. The bone response to grit blasted titanium (GB Ti) surfaces can be remarkably similar to that which occurs with calcium-phosphate-coated implants. While the topographies of these metallic and ceramic surfaces are similar the surface chemistries are very different. The purpose of this study was to ascertain the relative contributions of surface chemistry and topography to the bone forming tissue response to HA coated implants using an in vivo canine implant model. A canine femoral intramedullary implant model was used to compare the osseous response to identical c.p. titanium (Ti) implants that were either polished, grit blasted, plasma sprayed with hydroxyapatite (HA) or HA coated and covered with a thin layer of c.p. Ti by plasma vapor deposition (PVD-masked). The PVD-masked the chemistry of the underlying HA layer without changing its surface topography. Bone apposition averaged 3% for the polished implants and 23% for the grit blasted implants. Bone apposition to the HA-coated rods averaged 74% while bone apposition to the PVD-masked rods averaged 59%. These results clearly illustrate that topography is the dominant factor governing bone apposition. This is not to suggest that HA chemistry is irrelevant to the osseous response, but that it is of relatively minor benefit. The implications of this finding are wide ranging with respect to basic research and implant design.