EFFECTS OF HYDROXYAPATITE TRICALCIUM PHOSPHATE COATING AND INTRACANCELLOUS PLACEMENT ON BONE INGROWTH IN TITANIUM FIBERMETAL IMPLANTS

The purpose of this study was to compare the host-bone response to hyd roxyapatite/tricalcium phosphate (HA/TCP)-coated and noncoated titaniu m fibermetal implants placed in a load-sharing cancellous bone environ ment of the distal femurs of rabbits. The influence of implantation si te was also investigated by comparing these intracancellous implants w ith intramedullary implants evaluated in a previous study. Three param eters were measured: percentage implant perimeter surface length in co ntact with new bone, percentage internal fibermetal surface length in contact with ingrown bone, and percentage of available pore space fill ed with bone. The HA/TCP coating significantly accelerated and increas ed bone ongrowth, new bone formation on the perimeter and internal sur face of the implants. This effect was evident as early as 2 weeks afte r implantation. In contrast, there was no difference between HA/TCP-co ated and noncoated implants in the bone ingrowth parameter percentage of available pore space filled with bone, or pull-out strength. Scanni ng electron microscopy in the backscatter mode demonstrated that new b one formed directly onto the HA/TCP-coatcd fibers and did not usually form directly on noncoated fibers. Analysis of fluorochrome labeling r evealed that bone formation in weeks 1 through 4 was primarily woven a nd thereafter lamellar. Compared with intramedullary placement, intrac ancellous placement significantly accelerated the apposition of bone t o the perimeter and internal surface of HA/TCP coated implants and bot h accelerated and increased bone ingrowth as a percentage of available pore volume. These data show that the host response to titanium fiber metal implants is influenced both by HA/TCP coating and by the implant ation site.