[1] Seoul Natl Univ, Coll Med, Spine Ctr, Songnam 463707, South Korea
[2] Seoul Natl Univ, Coll Med, Dept Orthopaed Surg, Songnam 463707, South Korea
[3] Seoul Natl Univ, Bundang Hosp, Songnam 463707, South Korea
[4] Seoul Natl Univ, Coll Med, Dept Orthopaed Surg, Seoul, South Korea
[5] Seoul Natl Univ Hosp, Seoul 110744, South Korea
[6] Washington Univ, Dept Orthopaed Surg, St Louis, MO USA