[1] Univ Iowa, Iowa Spine & Brain Inst, Waterloo, ON, Canada
[2] Univ Calgary, Fac Med, Univ Calgary Spine Program, Dept Clin Neurosci, Calgary, AB, Canada
[3] Univ Alabama Birmingham, Childrens Hosp Alabama, Div Neurol Surg, Birmingham, AL USA
[4] Univ Maryland, Dept Neurosurg, Baltimore, MD 21201 USA
[5] Univ Maryland, Dept Orthopaed, Baltimore, MD 21201 USA
[6] Emory Univ, Dept Neurosurg, Atlanta, GA 30322 USA
[7] Barrow Neurol Inst, Div Neurol Surg, Phoenix, AZ 85013 USA
[8] Inova Hlth Syst, Dept Neurosci, Falls Church, VA USA