1. Department of Pediatric Orthopaedics, Deformity Reconstruction and Foot Surgery, University Hospital Muenster, Germany;
2. General Orthopaedics and Tumour Orthopaedics, University Hospital of Muenster, Germany;
3. Department of Research Methodology and Statistics in Psychology, University of Witten/Herdecke, Germany;
4. Danish Paediatric Orthopaedic Research, University Hospital Aarhus, Denmark