1. Division of Spine, Department of Neurosurgery, Duke University, Durham, NC 27710, USA
2. Institute of Spinal Pathology, Sao Paulo 04101000, SP, Brazil
3. Department of Neurosurgery, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, Buffalo, NY 14203, USA
4. Department of Neurological Surgery, University of California, La Jolla, San Diego, CA 92093, USA