[1] Seoul Natl Univ, Coll Med, Dept Neurosurg, Spine Ctr,Bundang Hosp, Seongnam 463707, South Korea
[2] Columbia Univ Coll Phys & Surg, Dept Orthopaed Surg, Spine Serv, New York, NY 10032 USA
[3] Univ Ulsan, Coll Med, Dept Neurosurg, Asan Med Ctr, Seoul 138736, South Korea