Bone bonding behavior of bead-coated alumina ceramic under load-bearing conditions

Alumina ceramic has good biocompatibility, high mechanical strength, and excellent lubrication properties. However, it is bioinert and does not bond with bone tissue. Therefore, to promote mechanical bonding, we have developed an alumina ceramic material coated with alumina ceramic beads using identical alumina ceramic binder. In this study, we evaluated the bone bonding capability of this material under load-bearing conditions along with its mechanical properties. The test pieces with or without bead-coating were implanted into the load-bearing portions of the medial and lateral femoral condyles of adult mongrel dogs. The dogs were euthanized 4, 8, and 24 weeks after implantation, and the pull-out test and histological examination were performed. The uncoated implants showed signs of loosening similar to those observed clinically. In contrast, the bonding strength of the bead-coated implants was significantly greater than that of the uncoated implants and increased with implantation time. This increase in strength differs from the results obtained in the non-load-bearing experiments, in which a plateau was seen relatively early after implantation. Results of histological examination suggested that this increase was caused by thickening of ingrown trabeculae, which could be observed as early as 4 weeks after implantation, at the bone-implant interface. In addition, the mechanical properties of the bead-coated alumina ceramic were comparable to those of grooved alumina ceramic which has been used clinically. These results indicate the possibility for clinical application of the bead-coated alumina ceramic.