1. Department of Neurological Surgery, Carolina Neurosurgery and Spine Associates, and Neurological Institute, Carolinas Healthcare System, Charlotte, North Carolina;
2. Department of Orthopedic Surgery and Neurological Surgery, Vanderbilt Spine Center,
3. Department of Orthopedic Surgery, Vanderbilt Spine Center, and
4. Department of Physical Medicine and Rehabilitation, Vanderbilt University Medical Center, Nashville, Tennessee;
5. Department of Neurological Surgery, Mayo Clinic, Rochester, Minnesota;
6. Department of Biostatistics, Vanderbilt University School of Medicine, Nashville, Tennessee;
7. Geriatric Research Education Clinical Center, Tennessee Valley Health System, Veterans Health Administration, Nashville, Tennessee;
8. Departments of Medicine and Biostatistics, Division of General Internal Medicine and Public Health, Center for Health Services Research, Vanderbilt University School of Medicine, Nashville, Tennessee;
9. Department of Neurosurgery, University of Virginia Medical Center, Charlottesville, Virginia; and
10. Department of Neurosurgery, University of Tennessee Health Sciences Center, Semmes-Murphey Neurologic & Spine Institute, Memphis, Tennessee