1. World Health Organization Collaborating Center for Public Health Aspect of Osteoarticular Disorders (O.B., J.D., J.-Y.R.), University of Liège, B-4000 Liège, Belgium
2. Department of Rheumatology (C.R.), University of Paris, Hôpital Cochin, 75014 Paris, France
3. Department of Clinique Générale Beaulieu (D.O.S.), CH-1206 Genève, Switzerland
4. Department of Rheumatology (T.D.S.), St. Thomas Hospital, London SE1 7EH, United Kingdom
5. Department of Service de Rhumatologie (P.F.), Hôpital Nord, 80080 Amiens, France
6. Odense University Hospital (K.B.), DK-5000 Odense, Denmark
7. Université Catholique de Louvain (J.-P.D.), Saint-Luc University Hospital, B-1348 Brussels, Belgium
8. Fundacion Jimenez Diaz (M.D.-C.), Servicio de Medicina Interna, Unidad de Metabolismo Oseo, 28029 Madrid, Spain
9. University of Rome La Sapienza (C.A.), 00185 Roma, Italy
10. Gent University Hospital (J.-M.K.), B-9000 Gent, Belgium
11. Department of Clinical Physiology (S.P.-N.), Hillerod Hospital, DK-3400 Hillerod, Denmark