1. Clinical Epidemiology and Research Center, Department of Biomedical Sciences; Humanitas University; Pieve Emanuele, Milan Italy
2. IRCCS Fondazione Don Carlo Gnocchi; Milan Italy
3. ISICO (Italian Scientific Spine Institute); Milan Italy
4. IRCCS Istituto Ortopedico Galeazzi; Milan Italy
5. Department of Epidemiology; Lazio Regional Health Service; Rome Italy
6. Department of Biomedical, Surgical and Dental Sciences; University La Statale; Milan Italy