1. University of Minnesota Medical School, Minneapolis, Minnesota;
2. Department of Neurosurgery, Vanderbilt University Medical Center, Nashville, Tennessee;
3. Department of Neurosurgery, Baylor College of Medicine, Houston, Texas;
4. Department of Orthopedic Surgery, Daniel and Jane Och Spine Hospital, Columbia University, New York, New York; and
5. Department of Radiology, Stanford University, Stanford, California