1. Department of Neurosurgery, Johns Hopkins University School of Medicine, Baltimore, Maryland;
2. Department of Neurosurgery, Yale University School of Medicine, New Haven, Connecticut;
3. Department of Neurosurgery, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts;
4. Department of Neurosurgery, Duke University Medical Center, Durham, North Carolina; and
5. Department of Orthopaedic Surgery, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts