[1] Hosp Trabajador, Santiago, Chile
[2] Clin Univ Los Andes, Santiago, Chile
[3] Univ Andres Bello, Hosp Trabajador, Fac Med, Santiago, Chile
[4] Sanat Guemes, BUENOS AIRES, Argentina
[5] Ctr Med Integral Fitz Roy, Buenos Aires, Argentina
[6] HOSP GEN AGUDOS DR TEODORO ALVAREZ, BUENOS AIRES, Argentina
[7] Hosp Clin Reg Concepcion, Dept Neurosurg, CONCEPCION, Chile
[8] Univ Concepcion, Fac Med, CONCEPCION, Chile
[9] Univ Campinas Unicamp, Campinas, Brazil
[10] Univ Passo Fundo, Passo Fundo, Brazil
[11] Univ del Desarrollo, Concepcion, Chile
[12] Clin Alemana, Dept Traumatol, Spine Unit, Santiago, Chile