Calvarial reconstruction in baboons with porous hydroxyapatite

The growth of bone into porous hydroxyapatite implanted in nonhealing calvarial defects of adult baboons is evaluated. Seventy-two anterior and posterior calvarial defects, 25 mm in diameter, were prepared in 24 adult male baboons (Papio ursinus). In each animal, one defect was implanted with a disc of porous hydroxyapatite obtained after hydrothermal conversion of the calcium carbonate exoskeleton of coral (genus Goniopora); pores averaged 600 microns in diameter, pore interconnections averaged 260 microns in diameter, and the void fraction was 70% (Interpore 500). Another defect was grafted with autogenous corticocancellous bone harvested from the iliac crest. The third defect was left ungrafted and used as a control. Histology and histomorphometry on nondecalcified and decalcified sections prepared from specimens harvested at 3, 6, and 9 months after surgery showed that substantial bone growth had occurred in the hydroxyapatite implants (p < 0.01 vs bone grafts at 3 mos), culminating in complete penetration of bone within the tridimensional porous spaces. Anterior untreated defects showed greater amounts of bone when compared to posterior defects. The extent of bone growth in hydroxyapatite implants, however, appeared to be independent of the site of surgical implantation. This finding suggests that bone deposition within the porous spaces was a function of the implanted matrix rather than the healing potential of specific regions within the calvaria. Of concern was the presence of nonunions at the hydroxyapatite/calvarial interfaces, despite the often extensive bone deposition within the center of the hydroxyapatite implants. Further studies are required to identify the reasons for nonunion and to evaluate the mechanical performance of the bone-porous matrix complex.(ABSTRACT TRUNCATED AT 250 WORDS)