[1] Vestre Viken Hosp Trust, Dept Radiol, N-3004 Drammen, Norway
[2] Innlandet Hosp Trust, Ctr Med Sci Educ & Innovat, Brumunddal, Norway
[3] Thrombosis Res Inst, London SW3 6LR, England
[4] Oslo Univ Hosp, Dept Biostat Epidemiol & Hlth Econ, Oslo, Norway
[5] Oslo Univ Hosp, Dept Cardiol, Ctr Clin Heart Res, Oslo, Norway
[6] Arhus Univ Hosp, Dept Orthopaed, Sect Traumatol, Aarhus, Denmark
[7] Vestre Viken Hosp Trust, Dept Biochem, N-3004 Drammen, Norway
[8] Univ Copenhagen, Glostrup Hosp, Copenhagen Spine Ctr, Glostrup, Denmark