A summation analysis of more than 70 individual kinematic studies involving normal knees and 33 different designs of total knee arthroplasty (TKA) was done with the objective of analyzing implant design variables that affect knee kinematics. Eight hundred eleven knees (733 subjects) were analyzed either during the stance phase of gait or a deep knee bend maneuver while under fluoroscopic surveillance. Fluoroscopic videotapes then were downloaded onto a workstation computer and anteroposterior (AP) femorotibial translational patterns were determined using an automated three-dimensional model fitting technique. The highest magnitude of translation was found in the normal and ACL-retaining TKA groups. Paradoxical anterior femoral translation during deep flexion was most commonly observed in PCL-retaining TKA. Substantial variability in kinematic patterns was observed in all groups. The least variability during gait was observed in mobile-bearing TKA designs, whereas posterior-stabilized TKA designs (fixed or mobile-bearing) showed the least variability during a deep knee bend. A medial pivot kinematic pattern was observed in only 55% of knees during deep knee flexion. Kinematic patterns of fixed versus mobile-bearing designs were similar with the exception of mobile-bearing TKA during gait in which femorotibial contact remained relatively stationary with minimal AP femorotibial translation.

The objective of the current study was to use fluoroscopy and computed tomography to accurately determine the three-dimensional, in vivo, weightbearing kinematics of five normal knees. Three-dimensional computer-aided design models of each subject's femur and tibia were recreated from the three-dimensional computed tomography bone density data. Three-dimensional motions for each subject then were determined for five weightbearing activities. During gait, the lateral condyle experienced -4.3 mm (range, -1.9--10.3 mm) of average motion, whereas the medial condyle moved only -0.9 mm (range, 3.4--5.8 mm). One subject experienced 5.8 mm of medial condyle motion. On average, during deep flexion activities, subjects experienced -12.7 mm (range, 1.4--29.8 mm) of lateral condyle motion, whereas the medial condyle motion only was -2.9 mm (range, 3.0--9.0 mm). One subject experienced 5.8 and 9.0 mm of medial condyle motion during gait and a deep knee bend, respectively leading to the occurrence of a lateral pivot motion. During the deep flexion activities, the subjects experienced significantly more axial rotation (> 13 degrees) than gait (< 5 degrees). During all five activities, the lateral condyle experienced significantly more anteroposterior translation, leading to axial rotation of the tibia relative to the femur.

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A method was developed for registering three-dimensional knee implant models to single plane X-ray fluoroscopy images. We use a direct image-to-image similarity measure, taking advantage of the speed of modern computer graphics workstations to quickly render simulated (predicted) images. As a result, the method does not require an accurate segmentation of the implant silhouette in the image (which can be prone to errors). A robust optimization algorithm (simulated annealing) is used that can escape local minima and find the global minimum (true solution). Although we focus on the analysis of total knee arthroplasty (TKA) in this paper, the method can be (and has been) applied to other implanted joints, including, but not limited to, hips, ankles, and temporomandibular joints. Convergence tests on an in vivo image show that the registration method can reliably find poses that are very close to the optimal (i.e., within 0.4 degrees and 0.1 mm), even from starting poses with large initial errors. However, the precision of translation measurement in the Z (out-of-plane) direction is not as good. We also show that the method is robust with respect to image noise and occlusions. However, a small amount of user supervision and intervention is necessary to detect cases when the optimization algorithm falls into a local minimum. Intervention is required less than 5% of the time when the initial starting pose is reasonably close to the correct answer, but up to 50% of the time when the initial starting pose is far away. Finally, extensive evaluations were performed on cadaver images to determine accuracy of relative pose measurement. Comparing against data derived from an optical sensor as a "gold standard," the overall root-mean-square error of the registration method was approximately 1.5 degrees and 0.65 mm (although Z translation error was higher). However, uncertainty in the optical sensor data may account for a large part of the observed error.