1. T. K. Timmers is a surgical trainee and L. P. H. Leenen is a trauma surgeon, Department of Surgery, University Medical Centre Utrecht, Utrecht, the Netherlands. M. H. J. Verhofstad is a trauma surgeon, Department of Surgery, St Elisabeth Hospital, Tilburg, the Netherlands. K. G. M. Moons is an epidemiologist, Department of Clinical Epidemiology, Julius Centre for Health Sciences and Primary Care, Utrecht, the Netherlands.