[Bone substitutes. State of the art and: what lies ahead?].

For the treatment of bony defects in the skeleton, today there are five different options. Filling a defect by the application of autogenous bone is one of them. Autogenous cancellous bone is still considered to be the gold standard, but numerous shortcomings of this material, described in detail in this paper, are not taken into account. Besides, we are still unable to influence bone healing by the transplantation of autogenous bone with reference to quality, quantity of newly forming bone and the time period, in which bone healing occurs. Investigation into the different kinds of biomaterial developed to replace autogenous bone as a transplant, and their implantation into experimental animals did not result in the production of a synthetic material that was as active as autogenous or even allogeneic cancellous bone. This was therefore not a solution to the problem. The reasons for this are multiple and are discussed in this paper. We developed a classification for bone replacement materials that differentiates between biological, synthetic, and composed materials, i.e., composite biomaterials made for bone replacement. In reference to the literature, as well as our own results, based on the implantation of more than 1200 rats, dogs, and sheep with distinct materials, the plus/minus effects of the different classes, groups and subgroups of bone replacement materials are summarized and discussed. The most recent knowledge about the mechanisms of bone formation and how it is influenced by different growth factors, as well as bioactive ceramics, indicates that in the future an applicable bone replacement material will be a composite of a carrier material combined with chemotactic, inductive, morphogenetic and proliferative, chemically pure, recombinant factors, with a mainly local action. Unfortunately, the road to get there is long.