[1] Brown Univ, Dept Orthopaed, Warren Alpert Med Sch, 1 Kettle Point Ave, East Providence, RI 02914 USA
[2] Brown Univ, Dept Orthoped, Biostat Div, Warren Alpert Med Sch, Grads Dorm Bldg 3rd Floor, Rhode Isl Hosp 593 Eddy, Providence, RI 02903 USA
[3] Univ Calif San Francisco, Dept Neurol Surg, Eighth Floor,400 Parnassus Ave, San Francisco, CA 94143 USA
[4] Duke Univ, Med Ctr, Dept Neurosurg & Orthopaed Surg, Durham, NC USA
[5] Univ Pittsburgh, Sch Med, Dept Neurol Surg, 200 Lothrop St, A402 UPMC Presbyterian, Pittsburgh, PA 15213 USA
[6] Swedish Neurosci Inst, 550 17th Ave, James Tower, Suite 500, Seattle, WA 98122 USA