1. Department of Neurosurgery, University of Toronto, Toronto, Ontario, Canada.
2. Department of Neurosurgery, Barrow Neurological Institute, Phoenix, Arizona.
3. Department of Neurosurgery, Thomas Jefferson University, Philadelphia, Pennsylvania.
4. Department of Orthopaedic Surgery, Université de Montréal, Montreal, Quebec, Canada.
5. Department of Neurosurgery, Mayfield Clinic, Cincinnati, Ohio.
6. Department of Neurological Surgery, University of Virginia, Charlottesville, Virginia.
7. Department of Orthopaedics, University of British Columbia, Vancouver, British Columbia, Canada.
8. Department of Orthopaedics, University of Washington, Seattle, Washington.