[1] Ajou Univ, Sch Med, Dept Neurosurg, Suwon, South Korea
[2] Yonsei Univ, Coll Med, Dept Neurosurg, Seoul, South Korea
[3] Yonsei Univ, Severance Hosp, Coll Med, Dept Neurosurg,Spine & Spinal Cord Inst, Seoul, South Korea
[4] Ilsan Hosp, Natl Hlth Insurance Serv, Dept Neurosurg, Goyang, South Korea
[5] Ilsan Hosp, Natl Hlth Insurance Serv, Res Inst, Goyang, South Korea