1. 1st Department of Orthopaedics, P. & A. Kyriakou Children’s Hospital, 115 27 Athens, Greece
2. Department of Hygiene, Epidemiology and Medical Statistics, Medical School, National and Kapodistrian University of Athens, 157 72 Athens, Greece
3. Medical School, National and Kapodistrian University of Athens, 157 72 Athens, Greece