1. 1Carolina Neurosurgery and Spine Associates, Charlotte;
2. 2Spine Institute of Louisiana, Shreveport, Louisiana;
3. 3Texas Back Institute;
4. 4Triangle Orthopedics Associates, Durham, North Carolina;
5. 5Plano Orthopedic Sports Medicine & Spine Center, Plano;
6. 6Gordon Spine Associates, Tyler, Texas; and
7. 7Olympia Medical Center, Los Angeles, California