Introduction: In an already published prospective and randomised study the positioning of TKA with and without a navigation device was analyzed. The results with navigation were significantly better than free hand surgery. The issue of this study was to find out if navigation can improve MIS in TKA.

Materials and methods: A three arm study was designed by the National Institute of Rheumatology. The study was prospective and externely evaluated. 30 persons have got TKA in an open technique with navigation, 30 cases have got MIS and another 30 MIS and navigation. Operation time, blood loss, early outcome and accuracy of the implantation was measured and compared.

Results: MIS increases the operation time and leads to a significant better early outcome within the first ten days. The accuracy of the implantation is poorer in comparison to open techniques. Navigation doesn‘t improve the results because the malpositioning is caused by the final surgical step of impaction. This was verified by a radiological score analysis using a score developed in our hospital for the postoperative X-rays.