[1] Univ British Columbia, Combined Neurosurg & Orthopaed Spine Program, Blusson Spinal Cord Ctr, Dept Orthopaed, Vancouver, BC V5Z 1M9, Canada
[2] Vancouver Gen Hosp, Combined Neurosurg & Orthopaed Spine Program, Vancouver, BC, Canada
[3] Univ Western Ontario, Dept Surg, Div Orthoped, London, ON N6A 3K7, Canada
[4] Univ Massachusetts, Dept Orthoped, Mem Med Ctr, Worcester, MA 01605 USA