1. Department of Orthopaedic Surgery Schulthess Clinic, Lengghalde 2, 8008 Zurich, Switzerland.
2. Department of Surgery Kantonsspital Graubünden, Loestrasse 170, 7000 Chur, Switzerland.
3. Department of Orthopaedics University of Duisburg-Essen, Pattbergstrasse 1-3, 45239 Essen, Germany.