1. Division of Neurosurgery, St. Michael's Hospital, University of Toronto, Toronto, Ontario, Canada.
2. Division of Neurosurgery, Toronto Western Hospital, University of Toronto, Toronto, Ontario, Canada.
3. Division of Spine Surgery, Vancouver General Hospital, University of British Columbia, Vancouver, British Columbia, Canada.
4. Division of Neurosurgery, University of Miami, Miami, Florida.
5. Division of Neurosurgery, Thomas Jefferson University Hospital, Philadelphia, Pennsylvania.
6. Division of Neurosurgery, Shock Trauma, University of Maryland, Baltimore, Maryland.
7. Division of Neurosurgery, University of Virginia, Chalottesville, Virginia.
8. Division of Neurosurgery, Methodist Hospital, Houston, Texas.