2-DIMENSIONAL RIGID-BODY KINEMATICS USING IMAGE CONTOUR REGISTRATION

A method for calculating two-dimensional rigid-body kinematic paramete rs using shape features is presented. Proposed applications include th e noninvasive quantification of planar joint motion in vivo. By using digitized images (computed tomographs, radiographs, etc.) of a bone co ntour at two positions, the contour curvatures can be 'best-fit' to ob tain a one-to-one mapping or registration of the bone images. This pro duces a dense field of displacement vectors from which planar rigid-bo dy kinematic parameters can be estimated. Accuracy was studied using r adiographic images of cadaveric femoral bone. The two motions of pure rotation with a fixed center of rotation and of pure translation were simulated. For pure rotation, error in rotation was independent of the rotation magnitude, with an average (n = 10) error of 0.3+/-0.8 degre es. The translation error averaged 0.9+/-0.5 mm. For pure translation, the error in rotation was -0.01+/-0.69 degrees and the error in trans lation was -0.62+/-0.98 mm (n = 10). This novel method has broad appli cations in the field of planar kinematics, especially in cases for whi ch marker fixation is neither possible nor practical.