1. University of Minnesota Medical School Twin Cities, Minneapolis, Minnesota, USA.
2. Department of Physical Medicine and Rehabilitation, MetroHealth Medical Center, Cleveland, Ohio, USA.
3. Department of Physical Medicine and Rehabilitation, Veteran Affairs, Minneapolis, Minnesota, USA.
4. Department of Biostatistics, University of Minnesota School of Public Health, Minneapolis, Minnesota, USA.
5. Department of Rehabilitation Medicine, University of Minnesota, Minneapolis, Minnesota, USA.
6. Department of Neurosurgery, University of Minnesota, Minneapolis, Minnesota, USA.
7. Department of Neurosurgery, Minneapolis VA Health Care System, Minneapolis, Minnesota, USA.
8. Department of Biomedical Engineering, University of Minnesota Twin Cities, Minneapolis, Minnesota, USA.
9. Department of Surgery, Hennepin County Medical Center, Minneapolis, Minnesota, USA.