POROUS-COATED VERSUS GRIT-BLASTED SURFACE TEXTURE OF HYDROXYAPATITE-COATED IMPLANTS DURING CONTROLLED MICROMOTION - MECHANICAL AND HISTOMORPHOMETRIC RESULTS

Hydroxyapatite (HA)-coated implants with porous-coated and grit-blaste d surface textures were inserted bilaterally in a paired design into t he medial femoral condyles of eight dogs for 16 weeks. The implants we re weight-loaded and initially subjected to controlled micromotion of 500 mu m during each gait cycle. Histology revealed that five implants in each group had bony anchorage, and the remaining implants were sur rounded by fibrous tissue. Push-out testing showed no difference in sh ear stiffness and strength, while energy absorption for porous-coated implants was increased significantly by threefold. The HA coating dela minated on grit-blasted implants during push-out testing, whereas poro us-coated implants predominantly failed at the HA-tissue interface. Co verage, surface area, volume, and thickness of the HA coating were sig nificantly reduced in vivo for porous-coated and grit-blasted implants . In conclusion, a plasma-sprayed porous-coated implant surface seems to give better fixation not only of the HA-coating to the implant surf ace but also of the implant to the surrounding tissues in comparison t o a grit-blasted implant surface. The HA coating was reduced more on f ibrous-anchored than on bony-anchored implants, suggesting that microm otion accelerates resorption of HA. Resorbed HA coating was replaced b y more bone on porous-coated implants than on grit-blasted implants, w hich suggests that fixation of porous-coated implants will be durable.