1. Orthopaedic Unit, S. Andrea Hospital, University of Rome, “La Sapienza” Via Di Grottarossa 1035, 00189 Rome, Italy
2. Division Orthopaedic Surgery, Ospedale San Paolo, 00053 Civitavecchia, Italy
3. Department of Orthopedic Surgery, Stanford University of School of Medicine, Stanford, CA 94063, USA