A theoretical and numerical approach to optimal positioning of the patellar surface replacement in a total knee endoprosthesis.

The clinical results of total knee joint arthroplasty with patellar replacement have shown that postoperative problems arise, especially under unfavourable biomechanical conditions. The findings concerning retropatellar contact forces have been obtained by means of different methods, partly through experimental investigations and partly through theoretical considerations. But so far patellar replacement criteria and the resulting changes of the retropatellar contact force were not taken into consideration in other studies. Our mathematical model is based on a mechanical one and the parameter study considers the influence of the height of the patellar surface replacement upon different biomechanical parameters at varying positions. The results suggest that the patellar replacement should therefore be kept as low as possible, thus reducing the retropatellar contact force to a minimum, especially in the extremely stressed flexion areas of up to about 90 degrees.