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-blasted surface textures were inserted bilaterally in a paired design into the medial femoral condyles of eight dogs for 16 weeks. The implants were weight-loaded and initially subjected to controlled micromotion of 500 microm during each gait cycle. Histology revealed that five implants in each group had bony anchorage, and the remaining implants were surrounded by fibrous tissue. Push-out testing showed no difference in shear stiffness and strength, while energy absorption for porous-coated implants was increased significantly by threefold. The HA coating delaminated on grit-blasted implants during push-out testing, whereas porous-coated implants predominantly failed at the HA-tissue interface. Coverage, surface area, volume, and thickness of the HA coating were significantly 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 surface but also of the implant to the surrounding tissues in comparison to a grit-blasted implant surface. The HA coating was reduced more on fibrous-anchored than on bony-anchored implants, suggesting that micromotion accelerates resorption of HA. Resorbed HA coating was replaced by more bone on porous-coated implants than on grit-blasted implants, which suggests that fixation of porous-coated implants will be durable.