1. Brown University, Providence, RI, USA
2. Oregon Health & Science University, Portland, OR, USA
3. Jefferson Medical College, The Rothman Institute, Philadelphia, PA, USA
4. University of California Los Angeles, Santa Monica, CA, USA
5. USC Spine Center, Los Angeles, CA, USA
6. University of Southern California, Los Angeles, CA, USA
7. Medstar Union Memorial Hospital, Baltimore, MD, USA
8. Johns Hopkins Medical Institutions, Baltimore, MD, USA
9. Mayo Clinic, Rochester, MN, USA
10. Kansas University Medical Center, Kansas City, KS, USA
11. Toronto Western Hospital, Toronto, Ontario, Canada
12. Cleveland Clinic, Cleveland, OH, USA
13. Columbia University, New York, NY, USA
14. New York-Presbyterian/The Allen Hospital, New York, NY, USA