1. Department of Biomedical Engineering, Duke University, 136 Hudson Hall, Box 90281, Durham, NC 27708 e-mail:
2. Department of Orthopaedic Surgery, Duke University, 375 Medical Science Research Building, Box 3093, Durham, NC 27710 e-mail:
3. Department of Biomedical Engineering and Orthopaedic Surgery, Duke University, 136 Hudson Hall, Box 90281, Durham, NC 27708 e-mail: