Hydroxyapatite-glass composite as a bone substitute in large metaphyseal cavities in rabbits

This study evaluated hydroxyapatite-glass (HA-G) composite as a filler material when implanted into a proximal metaphyseal tibial cavity consisting of medullary tissue and cancellous bone in rabbits. The repair process was compared with that of autogenous bone grafts and untreated controls. Scanning electron microscopy, energy dispersive x-ray studies, radiography, histology with tetracycline fluorescence and morphometric bone measurements were used for evaluation. Equal amounts of mineralised bone were produced in both HA-G granule and autograft groups at 3 weeks; thereafter, autografts mostly resorbed, whereas there was appositional lamellar bone formation on the early woven bone in the HA-group. A relatively small proportion of the cavities was repaired by new bone. The HA-G granules were biocompatible without foreign body reaction and showed good osteoconductive potential. Mesenchymal cells were able to differentiate into osteoblasts on bioactive surfaces of the composite. Although HA-G was able to form Ca-P-rich and Si-rich layers, most of the granules underwent degradation through its glass matrix, resulting in fewer bony contacts than granules with no surface degradation.