1. Department of Engineering, Dordt College, 498 4th Ave SE, Sioux Center, IA 51250 e-mail:
2. Sauk Prairie Memorial Hospital, Prairie du Sac, WI 53578 e-mail:
3. Department of Orthopedics and Rehabilitation, University of Wisconsin, Madison, WI 53705 e-mail:
4. Department of Biomedical Engineering, Department of Mechanical Engineering, University of Wisconsin, Madison, WI 53705 e-mail:
5. Departments of Orthopedics and Rehabilitation and Biomedical Engineering, University of Wisconsin, Madison, WI 53705 e-mail: