[1] Univ British Columbia, CORD, Vancouver, BC V6T 1Z4, Canada
[2] Univ British Columbia, Vancouver Gen Hosp, Dept Orthopaed, Div Spine, Vancouver, BC V5Z 1M9, Canada
[3] Univ British Columbia, Vancouver Gen Hosp, Dept Orthopaed, Div Orthopaed Engn Res, Vancouver, BC V5Z 1M9, Canada