Porous bioactive glass matrix in reconstruction of articular osteochondraldefects

Background and Aims: This study was carried out to investigate the use of p orous bioactive glass implants in promotion of articular cartilage and subc hondral bone repair in large osteochondral joint defects. Material and Methods: Two conical osteochondral defects (top diameter 3.0-3 .2 mm) were drilled into the patellar grooves of the distal femurs in the r abbit. The defects, extending (approximately 6-7 mm) from the surface of th e articular cartilage to the subchondral marrow space, were reconstructed w ith size-matched porous conical implants made of sintered bioactive glass m icrospheres (microsphere diameter 250-300 mu m, structural implant compress ion strength 20-25 MPa) using press-fit technique. The implant surface was smoothened to the level of the surrounding articular cartilage. One of the two defects in each femur was left empty to heal naturally and to serve as the control. At 8 weeks, the defect healing was analyzed with use of a semi quantitative histological grading system, histomorphometry of subchondral b one repair, back-scattered electron imaging of scanning electron microscopy (BEI-SEM), and a microindentation test for characterization for the stiffn ess properties of the cartilage repair tissue. Results: The porous structure of the bioactive glass implants, extending fr om the articular defect of the patellar groove into the posterior cortex of the femur, was extensively filled by new bone. Cartilage repair varied fro m near-complete healing by hyaline cartilage to incomplete healing predomin antly by fibrocartilage or fibrous tissue. There were, however, no statisti cal differences in the histological scores of repair between the glass-fill ed and control defects, although the sum of the averages of each category w as lowest for the bioactive glass filled defects. The indentation stiffness values of all the defects were also significantly lower than that of norma l cartilage on the patellar groove. Conclusions: Porous textures made by sintering bioactive glass microspheres may expand the opportunities in reconstruction of deep osteochondral defec ts of weight-bearing joints. The implants act mechanically as a supporting scaffold and facilitate the penetration of stromal bone marrow cells and th eir chondrogenic and osteogenic differentiation. Ionic properties of the bi oactive glasses make the substances highly potential even as delivery syste ms for adjunct growth factor therapy.