[Computer-assisted implant positioning in knee endoprosthetics. Kinematic analysis for optimization of surgical...

Modern approaches in knee endoprosthetics using computer-assisted navigation systems are based on matching procedures which refer to osseous anatomical landmarks. However, surface replacement techniques require a correct position of the implants in relation to the bone, as well as an optimal postoperative interaction of the ligaments and the surface design of the endoprosthesis. Functional aspects are of elementary importance. Insufficient design of the prosthetic surface or incorrect implantation overstresses ligamentous structures and result in functional disturbance, increased wear, and early loosening of the components. The present computer model permits a quantitative analysis of different implant positions. Distal positioning of the femoral component or insufficient resection of the tibial plateau results in a lag of extension. Increased distal resection of the tibial plateau produces marked translatory instabilities in the sagital plane which exceed the absolute height of the resection in millimeters. Monocondylar replacements with preservation of the ACL react kinematically more sensitively than bicondylar endoprostheses sacrificing the ACL. The results of this study are systematically summarized in an algorithm and indicate correction steps in order to avoid functional impairment. The computer model delivers in addition some basic data for optimized navigation procedures in knee surgery and demonstrates the importance of further developments in custom-made endoprosthetics.