Abstract
The development of new strategies for the engineering of bone regeneration requires appropriate model systems. Selection of the best model for testing a new technology depends on a host of factors. In general, the best model system is the one which most closely mimics the clinical situation for which this technology is being developed, will not heal spontaneously unless the technology is used, and will not heal when another technology is used if that technology is less advanced than the one being tested. For the purposes of developing new strategies for bone regeneration, systems which can be considered include those which model normal fracture healing, the segmental loss of bone or critical size defects, and various forms of nonunions in which fracture healing is perturbed either by mechanical, metabolic, or neurologic means. Careful experimental design and selection of the appropriate model system will enhance scientific efforts in bone regeneration research.