1. Division of Neurosurgery, Department of Surgery, Duke University Medical Center, Durham, NC, USA.
2. Department of Neurosurgery, University of Louisville, Louisville, KY, USA.
3. Center for Neurosurgical Outcomes Research, Maxine Dunitz Neurosurgical Institute Department of Neurosurgery, Cedars-Sinai Medical Center, Los Angeles, CA, USA.
4. Robley Rex VA Medical Center, Louisville, KY, USA.