[1] Univ Illinois, Carle Illinois Coll Med, Urbana, IL USA
[2] Dept Orthopaed Surg & Rehabil, Loyola Med, Maywood, IL USA
[3] Univ Minnesota Twin Cities, Dept Neurosurg, Minneapolis, MN USA
[4] Thomas Jefferson Hosp, Dept Neurosurg, Philadelphia, PA USA
[5] Rothman Orthoped Inst, Dept Orthoped Surg, Philadelphia, PA USA
[6] Carle Fdn Hosp, Dept Neurosurg, Urbana, IL USA
[7] Carle Fdn Hosp, Carle Illinois Coll Med, 610 N Lincoln Ave, Urbana, IL 61801 USA