HISTOLOGICAL AND MECHANICAL COMPARISON OF HYDROXYAPATITE-COATED COBALT-CHROME AND TITANIUM IMPLANTS IN THE RABBIT FEMUR

The purpose of this study was to compare hydroxyapatite (HA)-coated ti tanium (Ti) and HA-coated cobalt-chrome (CoCr) implants in the distal femur of the rabbit by evaluating bone apposition and interfacial shea r strength. Bilateral cylindrical implants with a plasma sprayed 50-mu m thick HA coating were press-fit into the metaphyseal cancellous bon e of the lateral femoral condyles in a transverse fashion, and the ani mals were sacrificed at 2, 4, and 8 weeks postimplantation. Mechanical strength of the interface between HA and bone was measured using the pushout method. For histologic analysis, the fractional linear extent of bone apposition was quantitated. No differences were found in the i nterfacial shear strength between the Ti and CoCr at any time period. The amount of bone apposition increased significantly at each time int erval for both substrate metals, but there were no significant differe nces between the two substrates at any of the time periods studied. Th e HA-coated CoCr implants performed in a similar manner to the HA-coat ed Ti implants, both mechanically and histologically, suggesting that HA-coated CoCr implants deserve further study as a viable alternative to Ti for the biological fixation of total joint components in orthopa edic surgery. (C) 1995 John Wiley & Sons, Inc.