IMPROVED FIXATION OF POROUS-COATED VERSUS GRIT-BLASTED SURFACE TEXTURE OF HYDROXYAPATITE-COATED IMPLANTS IN DOGS

We inserted, in 8 dogs, implants with either porous-coated or grit-bla sted titanium surface and coated with hydroxyapatite (HA) into trabecu lar bone in the proximal humerus, using a 1 mm gap model. After 25 wee ks, push-out tests showed that energy absorption for porous-coated imp lants was twice that of grit-blasted implants, whereas shear stiffness was reduced by one fifth, indicating a stronger fixation of porous-co ated implants. Macroscopically, all grit-blasted implants had delamina tion of the HA coating, whereas porous implants failed mostly at the H A-tissue interface. Porous-coated implants had 47% bone ingrowth and g rit-blasted implants 70% (p = 0.02), however, no difference in absolut e surface area was found. Part of the HA coating was resorbed during t he implantation period as regards volume and thickness. HA coverage wa s more reduced on porous-coated than on grit-blasted implants (p = 0.0 1). No foreign-body reaction or osteolysis was seen. An important find ing was that one fifth of the surface with complete resorption of HA c oating was replaced by newly formed bone.