Bone growth response with porous hydroxyapatite granules in a critical sized lapine tibial-defect model

This study evaluated the tissue reaction to porous hydroxyapatite (HA) granules in a critical sized tibial-defect of New Zealand white rabbits for a period of 2, 6, 12 and 24 weeks. Physicochemical characterizations of the granules were done using transmission electron microscopy, scanning electron microscopy, X-ray diffraction, and fourier transform infrared spectroscopy to analyse the microstructure, composition, phase purity crystallinity and functional groups of HA. Prior toin vivotesting, the HA granules had proved to be biocompatible and cytocompatibleen route in vitrostudies using L929 mouse fibroblast cells. In the histologic evaluation, as early as 2 weeks, bone ingrowth was observed in the pores and interstices of the granules forming a network of bony trabeculae and over 6, 12 and 24 weeks, it was seen that the granules assisted in bone formation. Fluorochrome multilabels of yellow, red and orange lines showed active sites of bone mineralization in progress in the pores and periphery of the granules. Good osteointegration of the granules with the host bone was observed. There was neither inflammation nor fibrous tissue interposition while resorption of the material was in effect a slow process, since the HA granules still persisted after 24 weeks.