When investigating orthopaedic biomaterials and tissue engineered devices, biological investigations by means of in vitro and in vivo tests are mandatory to obtain a overall picture of biocompatibility and therapeutic efficacy. However, various aspects requiring careful consideration should be kept in mind and can explain the complex situations encountered by researchers when the skeletal tissue is involved. This presentation aimed to summarize some useful information in improving in vivo methodology to test present and future therapies for orthopaedic surgery. Some in vivo biological tests to study innovative reconstructive surgical techniques are summarized on the basis of the experience of the Experimental Surgery Department –IOR. After in vitro and in vivo biocompatibility tests, for the study of bone defect healing and of biomaterial osteo-inductive properties the subcutaneous and intramuscular implants are usually performed in laboratory animals while osteoconduction and bone healing evaluation require the development of “nonunions” (sites that never achieve functional bone continuity) and “critical size defects” (the smallest defect that will heal with less than 10% bony growth) models. Biomaterial osteointegration properties are investigated by means of metaphyseal, diaphyseal and intramedullary implantation. The use of pathological animals is also recommended to take into account the clinical situation where biomaterials are often implanted in aged and osteoporotic patients. As far as articular cartilage pathology is concerned, chondral and osteochondral “critical size defects” may be performed and the development of osteoarthritic animals could be also useful. At different experimental times post-explantation evaluations by means of radiology, histology, histomorphometry and biomechanics provide a complete characterization of biomaterials and biotechnologies showing their potential therapeutic efficacy for skeletal reconstruction. In vivo studies provide important pre-clinical information on new biomaterials and biotechnologies for the skeletal reconstruction Among the factors that are increasingly improving the reliability of in vivo testing are the continuous improvement in knowledge on bone biology and comparative science between humans and animals, the awareness that animal suffering should be reduced as much as possible, and, finally, the amount and the accuracy of in vivo post-explantation findings.
