Comparison of enhancement of bone ingrowth into hydroxyapatite ceramics with highly and poorly interconnected pores by electrical polarization

The effects of electrical polarization of porous hydroxyapatite ceramics with different structures on bone ingrowth were compared. Two types of cylindrical porous hydroxyapatite ceramics with high and low interpore connection (hydroxyapatite-H and hydroxyapatite-L, respectively) were utilized in this study. Hydroxyapatite-H or hydroxyapatite-L with and without electrical polarization was implanted into the right or left femoral condyle of rabbits (n = 10 in each group) and histological examination was performed 3 and 6 weeks after operation. Each cross-section was divided into three regions, outer, middle and inner region, and the percentage of total newly formed bone area/total area of each region (% bone area) was calculated. Bone ingrowth throughout the region of implant was significantly larger in the hydroxyapatite-H group than in the hydroxyapatite-L group. Electrical polarization was effective in enhancing bone ingrowth through all the pores of hydroxyapatite-H implant, however, this advantage was not apparent in the hydroxyapatite-L implant. It is suggested that enhanced bone ingrowth into hydroxyapatite porous bodies due to electrical polarization may be a cooperative interaction between the osteoconductivity of hydroxyapatite porous bodies and enhanced osteogenic cell activity induced by large charges stored on the pore surfaces.