[1] Univ Pittsburgh, Dept Neurol Surg, Pittsburgh, PA 15260 USA
[2] NYU Langone Orthoped, Dept Orthoped Surg, New York, NY USA
[3] Hosp Special Surg, Dept Orthoped Surg, 535 E 70th St, New York, NY 10021 USA
[4] Vancouver Gen Hosp, Vancouver Spine Surg Inst, Vancouver, BC, Canada
[5] Washington Univ Orthoped, Dept Orthoped Surg, St Louis, MO USA
[6] Johns Hopkins Univ, Dept Orthopaed Surg, Baltimore, MD USA
[7] Univ Calif San Francisco, Dept Neurol Surg, San Francisco, CA USA
[8] Univ Calif San Francisco, Dept Orthopaed Surg, San Francisco, CA USA
[9] Brown Univ, Dept Orthopaed Surg, Providence, RI 02912 USA
[10] Univ Calif Davis, Dept Orthopaed Surg, Sacramento, CA 95817 USA
[11] Univ Virginia, Dept Neurol Surg, Charlottesville, VA USA
[12] Oregon Hlth & Sci Univ, Dept Orthopaed Surg, Portland, OR 97201 USA