[1] Univ Caxias do Sul, Lab Clin Studies & Basic Models Spinal Disorders, Dept Neurosurg, Caxias Do Sul, RS, Brazil
[2] Univ Caxias do Sul, Accountancy & Econ Sci Ctr, Caxias Do Sul, RS, Brazil
[3] Hosp Dr Diego E Thompson, Dept Orthopaed, Buenos Aires, DF, Argentina
[4] Vanderbilt Univ, Sch Med, Dept Neurosurg, Nashville, TN 37212 USA
[5] Washington Univ, Sch Med, Dept Neurol Surg, St Louis, MO USA