1. Steamboat Orthopaedic and Spine Institute, Steamboat Springs, Colorado;
2. Department of Orthopaedic Surgery, Vanderbilt University Medical Center, Nashville, Tennessee;
3. Neuroscience Institute, Carolina Neurosurgery & Spine Associates, Carolinas Healthcare System, Charlotte, North Carolina;
4. Department of Neurologic Surgery, Mayo Clinic, Rochester, Minnesota;
5. Departments of Neurological Surgery and Orthopedic Surgery, Duke University, Durham, North Carolina;
6. Department of Neurological Surgery, University of Utah, Salt Lake City, Utah;
7. Atlantic Neurosurgical Specialists, Morristown, New Jersey;
8. Department of Neurological Surgery, University of California, San Francisco, California; and
9. Department of Neurosurgery, University of Tennessee, Memphis, Tennessee