Øystein Rolandsen Riise1,2
, Eva Kirkhus3
, Kai Samson Handeland2
, Berit Flatø2
, Tor Reiseter4
, Milada Cvancarova5
, Britt Nakstad6,7
and Karl-Olaf Wathne1,8 
1
Department of Paediatrics, Ullevål University Hospital, Oslo, Norway
2
Department of Rheumatology, Rikshospitalet Medical Centre, Oslo, Norway
3
Department of Radiology, Rikshospitalet Medical Centre, Oslo, Norway
4
Department of Radiology, Ullevål University Hospital, Oslo, Norway
5
Department of Biostatistics, Rikshospitalet Medical Centre, Oslo, Norway
6
Department of Paediatrics, Akershus University Hospital, Nordbyhagen, Norway
7
University of Oslo, Akershus Faculty Division, Nordbyhagen, Norway
8
Ministry of Health and Care Services, Oslo, Norway