Spine (Phila Pa 1976). 2013 Oct 21. [Epub ahead of print]
Author information *Department of orthopedic surgery, Mayo Clinic, Rochester, MN, USA. **Center of orthopedic research and education (CORE) institute, Sun City West, AZ, USA. †Department of Orthopedic Surgery, Guang An Men Hospital, Beijing, China. ‡Department of orthopedic surgery, University of Hawaii, Honolulu, Hawaii, USA.