[1] Univ Toronto, Toronto Western Hosp, Dept Surg, Div Neurosurg, 399 Bathurst St, Toronto, ON M5T 2S8, Canada
[2] Univ Toronto, Toronto Western Hosp, Spinal Program, 399 Bathurst St, Toronto, ON M5T 2S8, Canada
[3] Keio Univ, Sch Med, Dept Orthopaed Surg, Shinjuku Ku, 35 Shinanomachi, Tokyo 1608582, Japan
[4] Nagoya Univ, Grad Sch Med, Dept Orthopaed Surg, Showa Ku, 65 Tsurumai Cho, Nagoya, Aichi 4668560, Japan
[5] Univ Toronto, Fac Med, Inst Med Sci, Med Sci Bldg,1 Kings Coll Circle,Room 2374, Toronto M5S IA8, ON, Canada