[1] Univ British Columbia, Dept Orthopaed, Div Spine, Vancouver, BC, Canada
[2] Thomas Jefferson Univ, Dept Orthopaed Surg, Philadelphia, PA 19107 USA
[3] Thomas Jefferson Univ, Dept Neurol Surg, Philadelphia, PA USA
[4] Rothman Inst, 925 Chestnut St,5th Floor, Philadelphia, PA 19107 USA
[5] British Columbia Childrens Hosp, Vancouver, BC, Canada
[6] Univ Calgary, Dept Surg, Calgary, AB, Canada
[7] Univ Calgary, Dept Clin Neurosci, Calgary, AB, Canada
[8] Univ British Coumbia, Vancouver Gen Hosp, Vancouver, BC, Canada
[9] Harvard Med Sch, Brigham & Womens Hosp, Dept Neurosurg, Boston, MA 02115 USA
[10] Yale Univ, Sch Med, Dept Orthopaed & Rehabil, New Haven, CT 06510 USA