1. Department of Health Sciences and Health Policy, University of Lucerne and Swiss Paraplegic Research, Frohburgstrasse 3, 6002 Lucerne, Switzerland
2. Swiss Paraplegic Research, Guido Zäch Institute, Guido Zäch Strasse 4, 6207 Nottwil, Switzerland
3. Rheumatology Unit, L. Sacco University Hospital, Via G.B. Grassi 74, 20157 Milan, Italy
4. Department of Internal Medicine, Policlinico Umberto I, Sapienza University of Rome, Via del Policlinico 155, 00161 Rome, Italy