1. Istituto Chirurgico Ortopedico Traumatologico (ICOT), Sapienza University of Rome, 00185 Rome, Italy
2. Istituto Fiorentino di Cura e Assistenza, 50139 Florence, Italy
3. University College London Hospital, London NW1 2BU, UK
4. The Princess Grace Hospital, London W1U 5NY, UK