1. Applied Biomechanics Laboratory, Department of Mechanical Engineering, University of Washington, Seattle, WA 98109
2. Cervical/Trauma Division, Medtronic Sofamor Danek, Inc., 710 Medtronic Parkway, Minneapolis, MN 55432
3. Barrow Neurosurgical Associates, 2910 N. 3rd Ave., Phoenix, AZ 85013