[1] Oregon Hlth & Sci Univ, Dept Neurol Surg, Mail Code CH8N,3303 SW Bond Ave, Portland, OR 97239 USA
[2] San Diego Ctr Spinal Disorders, La Jolla, CA USA
[3] Univ Michigan, Dept Neurosurg, Ann Arbor, MI 48109 USA
[4] Univ Calif San Francisco, Dept Neurol Surg, San Francisco, CA USA
[5] Henry Ford Hlth Syst, Dept Neurosurg, Detroit, MI USA
[6] Barrow Neurol Inst, Dept Neurosurg, Phoenix, AZ 85013 USA
[7] Great Lakes Neurosurg Associates, Grand Rapids, MI USA
[8] Spine Inst Louisiana, Shreveport, LA USA
[9] Scripps Clin Med Grp, Div Orthopaed Surg, La Jolla, CA USA
[10] Cedars Sinai Med Ctr, Orthoped, Los Angeles, CA 90048 USA
[11] Univ Pittsburgh, Dept Neurol Surg, Pittsburgh, PA 15260 USA