Rational Evaluation of Bone Grafts for Different Intraosseus and Heterotopic Implantations in Various Animal Models

Inflammation, repair and remodeling are part of the complex process of bone fracture healing. Impaired bone healing, however, should be treated using bone grafts or even bone material substitutes. These bone material substitutes have to be tested in vitro and in vivo before being applied in patients clinically. There are various large and small animal models known for testing different intraosseous and heterotopic implants of bone substitutes. Bone substitutes usually are being tested orthotopically for evaluation. However, literature suggests to start testing in small animals before large animal osseous defect models are being employed. Calvaria and femur in rat and rabbit models are the most commonly used defects sites for implantation, whereas defects of critical size vary considerably between animals. In all animals, heterotopic ossification can be found after implantation of bone substitute. However, most commonly the implantation of bone granules does not result in formation of new bone like tissue in small animals but in large animals only. Implantation of blocks of bone substitutes, however, do give rise to new bone like tissue in small and large animals. In this book chapter sites used for implantation of bone substitutes and animal bone defect models are critically evaluated and recommendations for future research are given.