In vivo fluoroscopic analysis of the normal human knee.

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.