1. Pediatric Orthopedic Department, Altona Children’s Hospital, Bleickenallee 38, D-22763 Hamburg, Germany
2. Department of Orthopedics, University Medical Center Hamburg-Eppendorf, D-20246 Hamburg, Germany
3. Center for Experimental Medicine, Institute for Medical Biometry & Epidemiology, University Medical Center Hamburg-Eppendorf, Chrisoph-Probst-Weg 1, D-20246 Hamburg, Germany