1. Department of Orthopaedics, Martina Hansens Hospital, Postboks 23, 1306 Baerum Postterminal, Norway
2. Innlandet Hospital Trust, 2381 Brumunddal, Norway
3. Thrombosis Research Institute, London SW36LR, UK
4. Department of Orthopaedics, Oslo University Hospital, Rikshospitalet, N-0027 Oslo, Norway