1 Department of Venous Surgery, Maastricht University Medical Centre, Maastricht, The Netherlands.
2 Department of Clinical Epidemiology and Medical Technology Assessment, Maastricht University Medical Centre, Maastricht, The Netherlands.
3 Department of Venous Surgery, Maastricht University Medical Centre, Maastricht, The Netherlands; Department of Vascular Surgery, Universitäts Klinikum, Aachen, Germany.