A simple fluoroscopy based technique for assessing 3D knee kinematics before, during, and after surgery

Kinematics of the normal, injured, or prosthetically replaced knee joint are a complex combination of rolling, gliding and rotational motions which are significantly influenced by the activity undertaken, the integrity of the ligaments and capsular structures, muscle activity, and articular geometry. Accurate kinematic information is critical to understanding the function and pathogenesis of the knee, particularly during weight bearing dynamic activities. In addition, intraoperative kinematic assessment during knee reconstruction would permit surgeons to objectively optimize graft placement and tensioning. The present study was undertaken to characterize the accuracy of a non-invasive fluoroscopic technique for measuring dynamic three-dimensional (3D) knee motions in individuals whose knees have not been prosthetically replaced, and demonstrate the measurement on in vivo step-up data. This technique utilizes orthogonal planar radiographic views of the knee to create a 3D contour model of consistently identifiable bony features for both the tibia and femur. The measurement technique is implemented by projecting the contour model onto digitized fluoroscopic images of the moving knee, and determining the translations and rotations which give the best correspondence between the projected contour model and the radiographic projection of the bone. Controlled in vitro assessment of the technique resulted in an average rotational accuracy of 1.1 degrees and a sagittal plane translational accuracy of 1.2 nun.