A. Magan et U. Ripamonti, GEOMETRY OF POROUS HYDROXYAPATITE IMPLANTS INFLUENCES OSTEOGENESIS INBABOONS (PAPIO-URSINUS), The Journal of craniofacial surgery, 7(1), 1996, pp. 71-78
Coral-derived porous hydroxyapatite disks of two geometric configurati
ons were implanted in 16 calvarial defects, 25 mm in diameter, prepare
d in eight subadult male baboons (Papio ursinus). To determine whether
the orientation of the exoskeletal microstructures (corallites) influ
ences bone ingrowth and osteogenesis, hydroxyapatite disks were prepar
ed by cutting the coral either longitudinally or transversally, to obt
ain two distinct implant geometries defined by the orientation of the
corallites. In the same animals, 16 defects were left untreated to ass
ess the regeneration potential of the subadult baboon calvaria. Disks
of both geometric configurations were also implanted in heterotopic in
tramuscular sites to investigate their osteoinductive potential. Histo
morphometric analysis on undecalcified and decalcified sections prepar
ed from specimens harvested on day 90 after surgery showed that greate
r amounts of bone formed in porous hydroxyapatites cut in the longitud
inal plane when compared with hydroxyapatites cut in the transversal p
lane (p < 0.01). Bone formed in hydroxyapatite specimens harvested fro
m the intramuscular sites, but no difference in bone formation was fou
nd between the two geometric configurations. Untreated defects showed
limited osteogenesis, comparable with a previous series of untreated d
efects identically prepared in adult baboon calvariae. This finding su
ggests that skeletally mature, adult primates may not be a requirement
for evaluation of craniofacial. bone substitutes. These results in a
primate indicate that hydroxyapatite disks are able to induce bone dif
ferentiation when implanted in intramuscular sites, and that the geome
tric configuration of the porous hydroxyapatite influences bone ingrow
th and osteogenesis in orthotopic calvarial sites. This should be take
n into consideration when designing porous bone substitutes for cranio
facial applications.