[Knee endoprostheses: problems and technological developments from the manufacturer's point of view]

Modern-day knee arthroplasty is based principally on the experience gained in the course of the past three decades. In the 1980s and 1990s, for example, the full constraint models of the 1970s were replaced by surface replacement prostheses with a combined rolling/sliding motion approximating the natural motion of the human knee joint for a wide range of applications. Not all of the relevant questions in the areas of material science, biomechanics, tribology, implant fixation and surgical technique have been fully explored by any means. Nevertheless, the medium-term and long-term results presently attained by knee arthroplasty are comparable to those achieved in the field of hip-joint arthroplasty. Although the success achieved by today's knee-joint prostheses is impressive, a critical analysis of therapeutic failures and complications is necessary to discover areas where further research is necessary and to formulate the challenges presenting themselves in R&D and in the manufacture of artificial knee joints. Currently, research efforts are focused on optimizing materials (especially in light of the presently unsatisfactory wear behavior of artificial knee joints), biomechanically-assisted design optimization to achieve a better harmonization between mobility and stability in the knee joint to be treated, alternative anchoring concepts, including consistently cement-free anchoring, and solutions for simplifying implantation techniques and making them more precise. The latter area, in particular, appears to be of great importance, since the quality of artificial knee joints and the long-term therapeutic outcome of knee-joint arthroplasty depend to a great extent on the correct alignment of the leg axes, an optimal implant position, and the correct adjustment of soft tissue tension. Technical innovations in this area of implant technology exert a multifactorial impact on different aspects of arthroplasty--e.g., uniform force transfer to minimize wear, selective rotation of the femoral components to optimize patella tracking, and avoidance of load concentrations to improve fixation strength--and thus form the basis for a surgical approach that takes greater account of "the big picture". Today's sophisticated navigation systems are a case in point. The non-imaging systems, in particular, have proved to be exceptionally useful; their advantages lie in their simple handling which makes use of common surgical techniques, the avoidance of additional imaging data recording (e.g. CT images), and an inconsequential increase in operation times.