1 From the Dartmouth Institute for Health Policy and Clinical Practice and Department of Orthopaedics, Dartmouth Hitchcock Medical Center, One Medical Center Dr, Lebanon, NH 03756-0001 (B.I.M.); and Department of Radiology, Department of Neurologic Surgery and Health Services, and Comparative Effectiveness, Cost and Outcomes Research Center, University of Washington, Seattle, Wash (J.G.J.).