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Severe knee injuries are reaching epidemic proportions in downhill skiing and are a major concern in other sports as well. Several experiments have used external joint motion measurement instruments to investigate the causes and mechanisms of knee injury. However, these measurements do not accurately represent the motion of the underlying bone (except under restricted test conditions) because of soft tissue motion of the transducer relative to the bone.
A new method is described that uses ultrasound imaging to quantify and account for soft tissue motion error by automatically tracking bone motion beneath the skin. The technique tracked in-plane motions of a lamb femur in its surrounding tissue with accuracies of 0.4 mm and 0.7 deg for motions within 10 mm and 6 deg, respectively, of an initial position. Errors in measurement of femur motion of a live test subject with an existing external transducer were computed with the method and were found to be large enough to suggest that these errors must be accounted for during in vivo tests.
ultrasound, kinematics, joint mechanics, motion analysis, soft tissue motion, biomechanics
Institute of Biomedical Engineering, Technical University of Berlin, Berlin,
Vice chancellor and professor of mechanical engineering, University of California, Berkeley, CA