Michael P Steinmetz MDWilliam P and Amanda C Madar Endowed Professor and Chair, Department of Neurological Surgery, Cleveland Clinic Lerner College of Medicine, Neurological Institute, Cleveland, Ohio, USAThomas E Mroz MDDirector, Centre for Spine Health; Director, Spine Research Lab, Centre for Spine Health; Departments of Orthopaedic and Neurological Surgery, Cleveland Clinic, Cleveland, Ohio, USAJeffrey C Wang MDChief, Orthopaedic Spine Service, Co-Director, USC Spine Centre; Professor of Orthopaedic Surgery and Neurosurgery, USC Spine Centre, Los Angeles, California, USA