*Department of Orthopaedics, University Medical Center Utrecht, Utrecht, The Netherlands†Department of Neurosurgery, Leiden University Medical Center, Leiden, The Netherlands‡Rehabilitation Center “De Hoogstraat,” Utrecht, The Netherlands§Department of Rehabilitation Medicine, Center for Rehabilitation, University Medical Center Groningen, Groningen, The Netherlands¶Department of Neurosurgery, University of Maryland, Baltimore, Maryland, USA||Department of Orthopedic Surgery and Sports Medicine, University of Washington Medical Center, Seattle, Washington, USA**Department of Orthopaedics, University of British Columbia, Vancouver, British Columbia, Canada††Division of Neurosurgery, Toronto Western Hospital, Toronto, Ontario, Canada‡‡Center for Spinal Surgery, BGU-Hospital, Frankfurt, Germany§§Department of Orthopaedic and Spine Surgery, Ganga Hospital, Coimbatore, Tamil Nadu, India¶¶Department of Orthopaedics, Thomas Jefferson University and Rothman Institute, Philadelphia, Pennsylvania, USA.