1. 1Departments of Orthopaedics and
2. 2Neurosurgery, University of Utah School of Medicine, Salt Lake City, Utah;
3. 3Department of Orthopedics and Rehabilitation Medicine, University of Wisconsin, Madison, Wisconsin;
4. 4University of Calgary Spine Program, Calgary, Alberta, Canada; and
5. 5Department of Orthopaedic Surgery, Thomas Jefferson University, Philadelphia, Pennsylvania