1. Clinic of Orthopaedic Surgery, University of Berne, Inselspital, 3010 Berne, Switzerland.
2. Department of Orthopaedics, Boston Medical Centre, 818 Harrison Avenue, Dowling, 2 North Boston, Massachusetts 02188, USA.
3. Department of Orthopaedic Surgery, Hôpital Cantonal, 1708 Fribourg, Switzerland.