1. ANCA Medical Center (AMC-Ghent), Krijgslaan 181, 9000 Ghent, Belgium.
2. UCLA/Orthopaedic Hospital, 2400 South Flower Street, Los Angeles, California 90007, USA.
3. Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences University of Oxford, Botnar Research Centre, Nuffield Orthopaedic Centre, Oxford OX3 7LD, UK.