1. Department of Orthopedic Surgery, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115.
2. Department of Orthopedic Surgery, University of Vienna, Vienna, Austria.
3. Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, Massachusetts.
4. Children's Hospital Medical Center, Boston, Massachusetts 02115.
5. Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139.
6. Rehabilitation Engineering Research and Development, Brockton/West Roxbury VA Medical Center, West Roxbury, Massachusetts 02132.