[Animal experiments for testing a hydroxyapatite ceramic coating under vacuum conditions]

Implants that were coated with hydroxyapatite ceramic (H-A.C.) under atmospheric condition in vivo often showed local areas of delamination. By applying the H-A.C. coating using the vacuum plasma spraying (VPS) technique, the mechanical characteristics of the coating was decidedly improved. We used a standardized rabbit model to compare a coating produced by this new technique with an implant conventionally plasma sprayed under atmospheric condition (APS). Cylindrical implants, 6 x 4 mm in size with a region flattened to a depth of 800 microns, were inserted into distal rabbit femurs underneath the patella. The flattened surfaces were coated with either a 150-micron APS-H-A.C. layer or a 150-micron VPS-H-A.C. layer plasma sprayed on an underlying 50-micron porous titanium layer. The animals were killed after 84 or 365 days. After 84 days histomorphologic evaluation revealed that more than 86% of each surface was covered with mature bone, while the VPS-H-A.C. coating demonstrated an almost two times greater tensile strength than the APS-H-A.C. coating. After 365 days both coatings showed a bony coverage of more than 94%. Again the tensile strength testing revealed much higher values for the VPS-H-A.C. coating. This study demonstrates that after 84 days as well as after 365 days in vivo, the VPS-H-A.C. coating had a significantly greater load capacity than an H-A.C. coating applied under atmospheric condition, and an equal affinity for bone.