Survival of onlay bone grafts. A study in the adult rat
Sammanfattning: The aim of this thesis was to study onlay bone grafting in the adult rat to improve graft incorporation and perservation of graft size. In 167 adult isogeneic lewis rats, the size maintenance and bone formation at the graft-host interface of uni- and bicortical onlays positioned in various environments and treatments were investigated. The findings were assessed after four, 12 and 20 weeks with routine histology and immunohistochemistry, using antibodies against some bone and cartilage matrix proteins and proteoglycans. The immunolabelling aimed to explore the possible occurence and localization of such proteins which are essential to various stages of osteogenesis and bone repair. The main findings were: Bicortical grafts were found to retain volume better than unicortical grafts and the exposed bone-marrow space of the graft was sealed off from the surrounding connective tissue by compact bone, emanating from the cortical margins of the graft. A major improvement in graft incorporation was observed following exposure of the underlying recipient marrow. On the other hand, these grafts were occasionally markedly submerged into the recipient bed, which was believed to be due to the disappearance of its pressure-resistant outer cortical layer. The effects of limited marrow exposure by cortical perforations of the recipient bed resulted in a migration of the recipient bone marrow into the graft as well as decreased graft size diminution. A combination of cortical perforations of a bicortical graft and the host bed entailed increased graft stability and corticalization of the marrow. When the graft was covered by an osteopromotive expanded polytetrafluoroethylene (e-PTFE) membrane, improved graft integration and greater size persistence was observed even after membrane removal. However, full volumetric maintenance of the graft was not accomplished in any of these studies. The combined treatment of the higher concentration (32µg/80µl) tested recombinant human bone morphogenetic protein-2 (rhBMP-2) and membrane lead to a rapid and complete graft integration and pronounced bone formation resulting in maintained or even enhanced graft size. In contrast, the application of high-dose rhBMP-2 without a membrane resulted in loss of graft size, extensive bone resorption and only small amounts of new bone formation. Therefore, when a collagen carrier is used for rhBMP-2 in conjunction with onlay bone grafting, our results indicate the advantage of applying a membrane to obtain graft volume persistence. The immunohistochemical labelling contributed to a more detailed picture of the mechanisms involved in graft incorporation and offered a dynamic indication of the bone repair and remodelling process as compared to routine histology.
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