1. Carolina Neurosurgery and Spine Associates, Charlotte;
2. Texas Back Institute; and
3. Spine Institute of Louisiana, Shreveport, Louisiana;
4. Triangle Orthopedics Associates, Durham, North Carolina;
5. Plano Orthopedic Sports Medicine and Spine Center, Plano;
6. Gordon Spine Associates, Tyler;
7. NeuroTexas, Austin;
8. Texas Back Institute Research Foundation, Plano, Texas