Total joint replacements, both in the hip and knee, are generally very successful operations. Still, however, component loosening as well as wear remains a problem, and all patients are not fully satisfied with their new joint. In a number of ongoing investigations, we are studying different factors involved in the fixation and function of the prosthesis components. We are exploring how to optimize the biomechanical joint conditions during surgery. We are evaluating new prosthesis designs and concepts and are in the frontline of surgery assisted by computer navigation. We have access to some of the very best evaluation techniques available for this type of research. Our patients are also followed up with both clinical and advanced radiographical examinations and a comprehensive package of outcome questionnaires. Our research aim at improving factors of importance for optimal implant fixation, function and survival, and not least for optimizing patient satisfaction and pain relief.