1. Department of Orthopaedic Surgery, VU Medical Center, Boelelaan, 1007 MB, Amsterdam The Netherlands
2. Nuffield Orthopaedic Centre, Windmill Road, OX3 7LD, Oxford UK
3. Great Ormond Street Hospital for Children, Institute of Child Health, University College London, London UK
4. Department of Paediatric Orthopaedic Surgery, University Children’s Hospital Basel (UKBB), Basel Switzerland