1. Unit of Clinical Epidemiology; IRCCS Galeazzi Orthopaedic Institute; Milan Italy
2. Unit of Clinical Epidemiology; IRCCS Istituto Ortopedico Galeazzi; Milano Italy
3. IRCCS Istituto Ortopedico Galeazzi; Milan Italy
4. Center of Biostatistics for Clinical Epidemiology, School of Medicine and Surgery; University of Milano-Bicocca; Monza Italy
5. Department of Physical Therapy; University of British Columbia; Richmond Canada
6. Department of Biomedical Sciences for Health; University of Milan; Milan Italy