1. *Norton Leatherman Spine Center, Louisville, Kentucky;
2. †Alan and Jacqueline Stuart Spine Center, Department of Neurosurgery, Lahey Hospital and Medical Center, Burlington, Massachusetts;
3. §Department of Neurosurgery, University of Tennessee Health Science Center and Semmes-Murphey Neurologic and Spine Institute, Memphis, Tennessee;
4. ¶Carolina Neurosurgery & Spine Associates, Charlotte, North Carolina