1. Department of Orthopaedic and Trauma Surgery, Ziekenhuis Hilversum, PO Box 10016, 1201 DA Hilversum, The Netherlands.
2. Department of Radiology
3. Department of Clinical Epidemiology and Biostatistics
4. Department of Orthopaedic Surgery, Academic Medical Centre, PO Box 22660, 1100 DD, Amsterdam, The Netherlands.