1. Department of Orthopaedics, Rehabilitation and Physical Therapy; Willem-Alexander Children's Hospital; Leiden University Medical Centre; Leiden The Netherlands
2. Department of Orthopaedic Surgery; Emma Children's Hospital; Academic Medical Center Amsterdam; University of Amsterdam; Amsterdam The Netherlands
3. Department of Paediatric Oncology/Haematology; Sophia Children's Hospital; Erasmus University Medical Center; Rotterdam The Netherlands
4. Department of Medical Statistics/Bioinformatics; Institute of Mathematics; Leiden University; Leiden The Netherlands