IRCCS Istituto Ortopedico Galeazzi, Unit of Clinical Epidemiology, Milan, Italy National Centre for Healthcare Research and Pharmacoepidemiology, Department of Statistics and Quantitative Methods, University of Milano-Bicocca, Milan, Italy; and Unit of Biostatistics, Epidemiology and Public Health, Department of Statistics and Quantitative Methods, University of Milano-Bicocca, Milan, Italy Istituto Superiore di Sanità, Centro Eccellenza Clinica, Qualità e Sicurezza delle Cure, Rome, Italy University of Maryland, Adams Cowley Shock Trauma Center, Maryland, USA Department of Pathophysiology and Transplantation, University of Milan, Milan, Italy; and General Surgery and Trauma Team, ASST Grande Ospedale Metropolitano Niguarda, University of Milan, Milano, Piazza Ospedale Maggiore, Milan, Italy.