1. M.C. Boonstra, PT, MSc, is a PhD student in the Orthopaedic Research Laboratory, Radboud University Nijmegen Medical Centre, Nijmegen, the Netherlands.
2. P.J.A. Schwering, MD, is Orthopaedic Surgeon, Department of Orthopaedics, Canisius-Wilhelmina Hospital, Nijmegen, the Netherlands.
3. M.C. De Waal Malefijt, MD, PhD, is Orthopaedic Surgeon, Department of Orthopaedics, Radboud University Nijmegen Medical Centre.
4. N. Verdonschot, PhD, is Professor and Head of the Biomechanics Department, Orthopaedic Research Laboratory, Radboud University Nijmegen Medical Centre, PO Box 9101, 6500 HB Nijmegen, the Netherlands. Dr Verdonschot also is Professor, Laboratory for Biomechanical Engineering, University of Twente, Department CTW, Enschede, the Netherlands.