[1] Univ Calif San Francisco, Dept Neurosurg, San Francisco, CA 94143 USA
[2] Univ Hong Kong, Dept Orthopaed & Traumatol, Li Ka Shing Fac Med, Pokfulam, Hong Kong, Peoples R China
[3] Univ Washington, Sch Med, Dept Orthoped & Sports Med, Seattle, WA USA
[4] Univ Utah, Sch Med, Dept Orthoped, Salt Lake City, UT USA
[5] Spectrum Res Inc, Tacoma, WA USA