Matthijs Paul Somford1, Daniël Hoornenborg2, Jan-Joost Wiegerinck3. 1. Department of Orthopedic Surgery, Medisch Spectrum Twente Enschede, Enschede, The Netherlands. Electronic address: mp_somford@hotmail.com. 2. Department of Orthopedic Surgery, Slotervaart ziekenhuis, Amsterdam, The Netherlands. 3. Department of Orthopedic Surgery, Academic Medical Centre, Amsterdam, The Netherlands.