1. Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts.
2. Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts.
3. Anatomical Institute, University of Kiel, Kiel, Germany.
4. Department of Clinical Sciences, Orthopaedic Research Center, Colorado State University, Fort Collins, Colorado.
5. Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts.