1 Department of Orthopaedic Surgery, Warren Alpert Medical School of Brown University, 2 Dudley Street. Providence, RI 02905, USA. Electronic address: Alan_Daniels@Brown.edu.
2 Department of Neurological Surgery, University of California San Francisco, 505 Parnassus Ave., Rm. M779, San Francisco, CA 94143, USA.
3 Department of Orthopaedic Surgery, University of California San Diego, Perlman Ambulatory Care Center, 9350 Campus Point Drive, La Jolla, CA 92037, USA.
4 Department of Neurological Surgery, University of Virginia, P.O. Box 800386, Charlottesville, VA, 22908, USA.
5 Department of Orthopaedic Surgery, Washington University, Cervical Spine Institute. 4921 Parkview Place, A12, St. Louis, MO 63110, USA.
6 Department of Orthopaedic Surgery, University of Wisconsin, 1685 Highland Ave., UWMFCB - 6215, Madison, WI 53705, USA.
7 Department of Orthopaedics and Rehabilitation, Oregon Health and Science University, 3181 SW Sam Jackson Park Rd., Portland, OR 97239, USA.