1. Department of Surgery, Spital Flawil, Kantonsspital St. Gallen, Krankenhausstrasse 23, 9230 Flawil, Switzerland
2. Department of Orthopaedic Surgery, University Hospital Balgrist, University of Zurich, Forchstrasse 340, 8008 Zurich, Switzerland
3. Computer Assisted Research & Development Group, University Hospital Balgrist, University of Zurich, Forchstrasse 340, 8008 Zurich, Switzerland