1. Department of Orthopaedic Surgery, New York University Hospital for Joint Diseases, New York, New York;
2. Department of Neurosurgery, University of Virginia Medical Center, Charlottesville, Virginia;
3. Rothman Institute, Egg Harbor Township, New Jersey;
4. Department of Neurosurgery, University of Kansas Medical Center, Kansas City, Kansas;
5. Department of Orthopaedic Surgery, University of Washington, Seattle, Washington;
6. Department of Neurosurgery, Toronto Western Hospital, Toronto, Ontario, Canada;
7. Emory Orthopaedics and Spine Center, Emory University School of Medicine, Atlanta, Georgia; and
8. Department of Neurosurgery, University of California-San Francisco Medical Center, San Francisco, California