1 David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California. Electronic address: vclark@mednet.ucla.edu.
2 College of Allied Health Professions, University of Nebraska Medical Center, Omaha, Nebraska.
3 Department of Orthopaedic Surgery, Harvard Medical School, Massachusetts General Hospital, Boston, Massachusetts.
4 University of Utah, Salt Lake City, Utah.
5 Department of Physical Medicine and Rehabilitation, Harvard Medical School; Massachusetts General Hospital, Brigham and Women's Hospital, and Spaulding Rehabilitation Hospital, Boston, Massachusets.