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Weight-bearing knee kinematics in patients who received two types of anterior cruciate ligament reconstruction were studied using a fluoroscopy-based three-dimensional measurement technique. Eleven patients with more than 1-year follow-up and good or excellent results participated in this study. Six subjects received anterior cruciate ligament reconstruction using a multiply folded semitendinosus and gracilis tendon graft, and five received combined intra- and extra-articular anterior cruciate ligament reconstruction using the iliotibial tract. The step up/down activity of normal and operated knees was recorded using lateral fluoroscopy. A customized three-dimensional contour model was created from two orthogonal views of each knee and all six degrees of freedom of knee movement were determined using a model matching technique. Both the normal and the reconstructed knees exhibited posterior condylar translation and internal tibial rotation with knee flexion, consistent with previous reports of normal kinematics. There were no statistically significant differences in the axial rotations or lateral or medial condylar anterior/posterior translations between operated and normal knees or between the two groups of operated knees.

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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. 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. 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 a rotational accuracy of 1.8 degrees and a sagittal plane translational accuracy of 1.2 mm.

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