Michael P Stauff1, Eugene J Carragee2. 1. Department of Orthopedics and Physical Rehabilitation, University of Massachusetts School of Medicine, Spine Center, Memorial Campus, 119 Belmont St, Worcester, MA 01605, USA. Electronic address: stauff@umassmemorial.org. 2. Department of Orthopedic Surgery, Stanford University School of Medicine, 450 Broadway Street, Pavilion C, MC 6342, Redwood City, CA 94063 USA.