[Biomechanics of cement-free endoprostheses]

At present only about 20 per cent of endoprosthetic stems and 30 per cent cups are implanted without cement. Nevertheless, the number of modifications and new developments in cementless endoprosthetics is continuously growing. Years ago bone cement was made responsible for all failures, but meanwhile the approach to it got more differentiated. The advantages of cement fixation in case of elderly patients as well as those of cementless implantation for patients where revision operation could be expected were recognized. Whereas sufficient primary stability can be generally achieved without any problem in case of cement implantation, the cementless one needs more intensified planning as well as a different surgical technique. Today not only torsional stability and stiffness of stem and bone implant are discussed more intensively than before but also new anchorage concepts as for example tubular stems or custom made systems. Obviously, the existing screw cups and clamp/clip systems are more in demand than cementless stem systems. The results of different coatings and surface modifications are rather inhomogeneous and there is a need of more basic research in this respect.