[1] UCL, Natl Hosp Neurol & Neurosurg, Dept Neurosurg, London, England
[2] UCL, Inst Neurol, London, England
[3] UCL, Dept Epidemiol & Publ Hlth, London, England
[4] Thomas Jefferson Univ & Hosp, Dept Orthoped, Philadelphia, PA USA
[5] Thomas Jefferson Univ & Hosp, Dept Neurosurg, Philadelphia, PA USA
[6] Aarhus Univ Hosp, Dept Orthopaed Surg, DK-8000 Aarhus, Denmark
[7] Univ Toronto, Div Neurosurg, Toronto, ON, Canada
[8] Univ Toronto, Spinal Program, Toronto, ON, Canada
[9] Toronto Western Hosp, Toronto, ON M5T 2S8, Canada
[10] Kanazawa Univ, Dept Orthopaed Surg, Kanazawa, Ishikawa, Japan
[11] Hosp Univ Dr Peset, Spinal Unit, Valencia, Spain
[12] Inst Mutualiste Montsouris, Dept Orthopaed Surg, Paris, France
[13] Univ Med Ctr Utrecht, Dept Orthopaed Surg, Utrecht, Netherlands
[14] LUMC, Dept Neurosurg, The Hague, Netherlands
[15] Med Ctr, The Hague, Netherlands
[16] Univ Miami, Miller Sch Med, Dept Neurosurg, Miami, FL 33136 USA