1. Mem. ASME Department of Orthopaedic Surgery, Washington University, St. Louis, MO 63110 e-mail:
2. Department of Earth and Planetary Sciences, Washington University, St. Louis, MO 63110 e-mail:
3. Mem. ASME Department of Mechanical Engineering and Materials Science, Washington University, St. Louis, MO 63110 e-mail:
4. Mem. ASME Department of Orthopedic Surgery, Columbia University, New York, NY 10032;
5. Department of Biomedical Engineering, Columbia University, New York, NY 10032 e-mail: