1. Departments of Neurological Surgery,
2. Public Health Services, and
3. Center for Health Policy and Health Services Research, Henry Ford Health, Detroit, Michigan;
4. Departments of Neurosurgery and
5. Orthopedics, University of Michigan, Ann Arbor, Michigan;
6. Department of Orthopedics, William Beaumont Hospital, Troy, Michigan; and
7. Departments of Orthopedics and
8. Neurosurgery, William Beaumont Hospital, Royal Oak, Michigan