1. Department of Neurological Surgery, University of California San Francisco, San Francisco, California, USA;
2. Department of Neurological Surgery, Tufts Medical Center, Boston, Massachusetts, USA;
3. Department of Orthopaedic Surgery, University of California San Francisco, San Francisco, California, USA;
4. Division of Cardiothoracic Surgery, Department of Surgery, University of California San Francisco, San Francisco, California, USA