[1] Univ British Columbia, Dept Orthopaed, Div Spine, Vancouver, BC V5Z 1M9, Canada
[2] Thomas Jefferson Univ, Dept Orthopaed Surg, Philadelphia, PA 19107 USA
[3] Thomas Jefferson Univ, Dept Neurol Surg, Philadelphia, PA 19107 USA
[4] Rothman Inst, Philadelphia, PA USA
[5] Yale Univ, Sch Med, Dept Orthopaed & Rehabil, New Haven, CT 06510 USA
[6] British Columbia Childrens Hosp, Vancouver, BC V6H 3V4, Canada
[7] Univ Calgary, Dept Surg, Calgary, AB, Canada
[8] Univ Calgary, Dept Clin Neurosci, Calgary, AB, Canada
[9] Harvard Univ, Brigham & Womens Hosp, Sch Med, Dept Neurosurg, Boston, MA 02115 USA
[10] Northwestern Univ, Feinberg Sch Med, Dept Orthopaed Surg, Chicago, IL 60611 USA