1. Orthopaedic Department, University Hospital, University of Duisburg-Essen, Hufelandstrasse 55, D-45147 Essen, Germany.
2. Department of Mechanical Engineering, Department of Surgery, and Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, ON K1N 6N5, Canada; Department of Mechanical Engineering, University of Ottawa, 161 Louis Pasteur A-206, Ottawa, ON K1N 6N5, Canada.
3. Department of Orthopaedic Surgery, University of Massachusetts Medical School, 55 Lake Avenue North, Worcester, MA 01655, USA.