Animal models relevant to cementless joint replacement.

This review focuses on animal models used to study certain aspects of 'cementless' joint replacement. Implants used in this application are designed to become attached to the host skeleton through either bone ingrowth into porous surfaces or bone apposition (ongrowth) onto other types of surfaces. Biological fixation of cementless joint replacement implants relies on intramembranous bone regeneration. We describe a framework for understanding research design in light of the type of research questions now being asked. In particular, species choice, implant design and placement, and experimental endpoints are described in some detail. We provide a summary of recent studies specifically focused on implant fixation, demonstrating that most work is still at the morphological and biomechanical levels with little understanding at the molecular level. We also provide a more comprehensive listing of studies using hip and knee replacement models, demonstrating that most work is focused on the interface, and responses of the immediately adjacent trabecular bone and the more distant cortical bone. We conclude by encouraging investigators to design their experiments so that there is enough power to answer a limited number of questions as opposed to providing limited data on a broader number of issues.