1. Surgical Outcomes Research Center, University of Washington, Seattle
2. Department of Orthopaedic and Sports Medicine, University of Washington, Seattle
3. Swedish Neuroscience Institute, Swedish Medical Center, Seattle, Washington
4. Valley Medical Center, Renton, Washington
5. Skagit Northwest Orthopedics, Proliance Surgeons, Inc, Mount Vernon, Washington
6. Franciscan Neurosurgery Associates at St Joseph, CHI Franciscan Health, Tacoma, Washington
7. Rainier Orthopedic Institute, Proliance Surgeons, Inc, Puyallup, Washington
8. Department of Anesthesiology and Pain Medicine, University of Washington, Seattle
9. Department of Surgery, University of Washington, Seattle