1. Orthopaedic Department G-4-N, Academic Medical Centre, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands.
2. University Hospital, POB 9101, 6500 HB Nijmegen, The Netherlands.
3. Refaja Hospital, Boerhaavestraat 1, 9501 HE Stadskanaal, The Netherlands.