1. Institute for Spinal Disorders, Cedars-Sinai Medical Center, Los Angeles, California;
2. Wilderness Spine Services, Columbus, Georgia;
3. Central Texas Spine Institute, Austin, Texas;
4. The Orthopedic Center of St. Louis, Missouri;
5. Orthopedic Specialists, Allentown, Pennsylvania; and
6. Center for Sports Medicine & Orthopaedics, Chattanooga, Tennessee