A Courvoisier1, E Bourgeois2, C Durand3, J Griffet2. 1. University Clinic of Paediatric Surgery, Paediatric Orthopaedics, Hôpital Couple-Enfant, Grenoble University Hospital, Joseph-Fourier University, BP 217, 38043 Grenoble cedex 09, France. Electronic address: acourvoisier@chu-grenoble.fr. 2. University Clinic of Paediatric Surgery, Paediatric Orthopaedics, Hôpital Couple-Enfant, Grenoble University Hospital, Joseph-Fourier University, BP 217, 38043 Grenoble cedex 09, France. 3. University Clinic of Paediatric Radiology, Hôpital Couple-Enfant, Grenoble University Hospital, Joseph-Fourier University, BP 217, 38043 Grenoble cedex 09, France.