[1] Univ Toronto, Temerty Fac Med, Toronto, ON, Canada
[2] Univ Toronto, Div Neurosurg, Toronto, ON, Canada
[3] Univ Toronto, Dept Surg, Spine Program, Toronto, ON, Canada
[4] Univ Hlth Network, Krembil Neurosci Ctr, Toronto, ON, Canada
[5] Thomas Jefferson Univ, Dept Neurosurg & Orthoped Surg, Philadelphia, PA USA
[6] Jefferson Hosp Neurosci, Philadelphia, PA USA
[7] Univ Maryland, Dept Neurosurg, Div Biostat & Bioinformat, Sch Med, Baltimore, MD USA