Orthopaedic Department, The Royal Children's Hospital, 50 Flemington Road, Parkville, Victoria 3052, Australia. Murdoch Childrens Research Institute, The Royal Children's Hospital, Victoria, Australia. Department of Paediatrics, University of Melbourne, The Royal Children's Hospital, Victoria, Australia. CanChild Centre, McMaster University, Hamilton, Ontario, Canada. Departments of Epidemiology, Biostatistics and Pediatrics, and Human Development, College of Human Medicine, Michigan State University, East Lansing, Michigan, USA. Department of Neurology, Université Libre de Bruxelles (ULB), Brussels, Belgium. Complex Motor Disorders Service, Evelina Children's Hospital, London, UK. Rehabilitation Medicine Department, National Institutes of Health, Bethesda, Maryland, USA. Department of Rehabilitation Medicine, VU University Medical Center, Amsterdam, The Netherlands. Department of Physical Medicine and Rehabilitation and Pediatrics, Feinberg Northwestern School of Medicine, Rehabilitation Institute of Chicago, Chicago, Illinois, USA. Institute of Health and Society, Newcastle University, Newcastle upon Tyne, UK. Developmental Disability and Rehabilitation Research, Murdoch Childrens Research Institute, The Royal Children's Hospital, Victoria, Australia. Rehabilitation Institute of Chicago, Chicago, Illinois, USA.