1. Department of Neurological Surgery, Washington University in St. Louis, St. Louis, Missouri;
2. Department of Neurological Surgery, University of Miami Miller School of Medicine, Miami, Florida;
3. Department of Neurosurgery, University of Utah, Salt Lake City, Utah;
4. Department of Neurological Surgery, University of California, San Francisco, California;
5. Department of Neurosurgery, University of Florida, Gainesville, Florida;
6. Departments of Orthopedic Surgery and
7. Department of Neurological Surgery, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania;
8. Department of Orthopedic Surgery, University of California, Davis, Sacramento, California;
9. Department of Orthopedic Surgery, University of Chicago, Chicago, Illinois;
10. Department of Neurosurgery, University of Michigan, Ann Arbor, Michigan;
11. Neurosurgery, University of Maryland Medical Center, Baltimore, Maryland;
12. Department of Neurosurgery, Duke University, Durham, North Carolina; and
13. Department of Neurosurgery, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania