1. Department of Neurosurgery, The Johns Hopkins University School of Medicine, Baltimore, Maryland, United States
2. Department of Neurosurgery, Mayo Clinic, Rochester, Minnesota, United States
3. Department of Orthopaedics, Division of Spine, University of British Columbia and Vancouver General Hospital, Vancouver, British Columbia, Canada
4. Department of Neurological Surgery, Memorial Sloan-Kettering Cancer Center, New York, New York, United States
5. Division of Orthopaedic Surgery, McGill University, Montreal, Quebec, Canada