Incorporation and biodegradation of hydroxyapatite-tricalcium phosphate implanted in large metaphyseal defects--an...

Incorporation and biodegradation of hydroxyapatite(HA)-tricalcium phosphate(TCP) granules implanted in 5 x 5 x 5 mm distal femoral metaphyseal defects created in 18 adult rabbits were studied. In two rabbits, the defects were left to heal spontaneously without any implant. Roentgenographic and histological study by light microscopy was done on silver nitrate stained undecalcified sections as well as haematoxylin-eosin stained decalcified sections. The synthetic HA-TCP was biocompatible and produced no adverse reactions. The implant was osteoconductive and allowed good new bone formation to occur, mainly from periphery to center, but mature trabeculae could be delineated only at 4-6 months. The HA-TCP biomaterial had very low biodegradability with marked amount of intact implant still present at final follow up. Bonding between implant and bone, though a close biological bond, was not uniformly strong. Rate of bone ingrowth was very slow and large areas of implant at center did not show new bone formation at 12 months.