ABSTRACT
The principle of bone grafting is to provide an osteoconductive surface which will allow bone to grow from the graft recipient into and through the defect where bone repair is required. This is followed by a process of remodeling, leading to the appropriate distribution of new bone and the resorption of the graft. The major types of bone graft in use are autograft, fresh-frozen and freeze-dried allograft, and demineralized bone. There are, however, important differences between these graft materials that lead to differences in outcome, and these are, in part, a consequence of the cellular component of the graft (Schwarz et al. 1991, Graham et al. 2010). Autograft is generally accepted as the most effective bone repair material, but it has a limited supply and requires surgical harvest, producing comorbidity in the patient. Allograft bone is available in larger quantities, and the techniques of freezing and freeze drying allow storage prior to use; however, clinical outcome is more variable (McGarvey and Braly 1996). While freezing produces death and breakup of the cellular component of the graft, it does not fully remove the immunogenicity of the graft (Strong et al. 1996, VandeVord et al. 2005). In addition, the loss of cells removes the osteogenic component which is conferred on autograft by the presence of mesenchymal progenitor cells (MPCs) present on the bone surfaces. Demineralized bone matrix (DBM) contains no cells, and while this removes antigenicity and can provide osteoconductive and osteoinductive properties, there is no osteogenic component. Research and development of bone graft substitute materials has been extensive, and
some of these materials have entered routine clinical practice (Bueno and Glowacki 2009). Typically, they provide a scaffold material with a surface that allows a good osteoconductive response with various additional benets ranging from biodegradability, intrinsic osteoinductivity and the ability to be combined with osteoinductive growth factors. However, as with allograft and demineralized bone, there are no endogenous cells, and there is a lack of the osteogenic response they engender. Used alone, these materials rely on the cells present in the implant site and the surrounding bone and those brought in by invading blood vessels to enable a repair response. Some of these materials are able to elicit bone formation, although this is generally less than with autograft; however, recently, there has been evidence presented that certain ceramic materials are able to produce equivalent repair to that seen with autogeneic bone (Yuan et al. 2010).
