1. Dept. of Physical Medicine and Rehabilitation, Tufts University School of Medicine, Boston, MA 02111, USA
2. Department of Orthopedics, Mount Sinai School of Medicine, New York, USA
3. Litterst & Associates, Newton, MA, USA
4. Dept. of Orthopedics, Mount Sinai School of Medicine, New York, and Dept. of Biomedical Engineering, Columbia University, New York, USA