3D kinematics of normal knee using X-ray fluoroscopy and CT images.

In orthopaedics, quantitative assessment of dynamic knee kinematics under in vivo conditions is very important for understanding the effects of joint diseases, dysfunction and for evaluating the outcome of surgical procedures. This study presents a method to determine 3D kinematics of normal knee using X-ray fluoroscopy. 3D poses of normal knee are estimated using a feature-based 2D/3D registration technique, which uses bone contours on fluoroscopic images and 3D bone polygonal surface model of femur, tibia/fibula, and patella. The 3D bone models for each normal knee were created using CT scan data from a single subject. An objective function is defined as the sum of Euclidean distance from point on the projection rays (corresponding to the point on the contours) to the closest point on the bone model surface. The 3D pose of the bone model is estimated by minimizing the objective function iteratively with a non-linear optimization technique. In the 3D kinematic analsysis of normal knee, the relative pose of the femur with respect to tibia/fibura was determined by employing a three-axis Euler-angle system. In order to validate the pose estimation accuracy of normal knee, computer simulation test was performed. A set of 5 synthetic silhouette images was created for each bone model in known typical orientations. Errors in the 3D pose of the model were determined by comparing the estimated pose to the known pose. The result of computer simulation test showed that the root mean square errors were within 1.0mm, 1.0°except for out-of-plane translation for femur, tibia/fibula. While, for patella, rotation errors were increased. In clinical application, dynamic movement under loaded conditions was test. The result of knee kinematics showed a smooth and reasonable physiologic pattern, and the reliability and feasibility of present method was demonstrated. [ABSTRACT FROM AUTHOR]