1. Department of Surgery, Johns Hopkins University School of Medicine, Baltimore, MD, USA
2. Johns Hopkins, University School of Medicine, Baltimore, MD, USA
3. Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA
4. Department of Surgery, University of Wisconsin School of Medicine and Public Health, Madison, WI, USA
5. Center for Health Services and Outcomes Research, Northwestern University Feinberg School of Medicine, Chicago, IL, USA
6. Department of Surgery, Northwestern University Feinberg School of Medicine, Chicago, IL, USA
7. Department of Surgery, New York University, New York, NY, USA
8. Department of Orthopaedic Surgery, University of Pennsylvania, Philadelphia, PA, USA