[1] OR Hlth & Sci Univ, Oregon Evidence Based Practice Ctr, Dept Med, Portland, OR USA
[2] Med Coll Wisconsin, Dept Neurosurg, Milwaukee, WI 53226 USA
[3] Stanford Univ, Dept Orthoped Surg, Stanford, CA 94305 USA
[4] Univ Wisconsin, Dept Neurosurg, Madison, WI USA
[5] Univ Kentucky, Dept Orthopaed, Lexington, KY USA
[6] Univ Washington, Dept Neurol Surg, Seattle, WA 98195 USA