INTRAMEDULLARY IMPLANT OF PLASMA-SPRAYED HYDROXYAPATITE COATING - AN INTERFACE STUDY

An intramedullary implant model in the canine femora was developed to evaluate the mechanical and histological responses between cancellous bone and plasma-sprayed hydroxyapatite coatings (HACs) on Ti-6A1-4V im plants, with 12- and 24-week follow-ups. HACs of different thicknesses were investigated. Results of the mechanical testings revealed that a fter 24 weeks of implantation, the mean shear strength (2.49 +/- 0.12 MPa) of the 50 mu m HACs was significantly higher (p < 0.05) than that of the 200 mu m HACs (1.44 +/- 0.19 MPa). However, using backscattere d electron images (BEIs) throughout all the implant periods, no substa ntial histological variations in the extent of new bone apposition bet ween the two HACs were observed. Occasionally, solution-mediated disin tegration of the 50 mu m HAC was found 24 weeks postimplantation. Hist omorphometric studies from the BEIs demonstrated that for both HACs th e percentage of the direct HAC-cancellous bone contact was approximate ly 50% at 12 weeks and 75% at 24 weeks. After the mechanical tests, th e 200 mu m HACs had fracture sites either inside the coating layers or at the HAC-titanium interfaces, which might explain why the mechanica l performance of the 200 mu m HACs was inferior to that of the 50 mu m HACs even though both HACs had the same histological behaviors. (C) 1 997 John Wiley & Sons, Inc.