IN-VIVO KINEMATIC ANALYSIS OF A MOBILE BEARING TOTAL KNEE PROSTHESIS

Ten normal subjects and 10 patients with a posterior cruciate retainin g mobile bearing total knee replacement performed successive deep knee bends under fluoroscopy to determine tibiofemoral contact positions, At full extension the average initial contact position for the normal and mobile total knee replacement was 6.2 mm (range, 4.8 to 12 mm) ant erior, and -4.4 mm (range, 3.9 to 11 mm) posterior to the sagittal tib ial midplane, respectively, At 60 degrees flexion, the normal knee rol led back to -5.8 mm (range, -2.5 to -13.2 mm), whereas the mobile bear ing total knee replacement rolled back to -9.2 mm (range, -4 to -17 mm ), From 60 degrees to 90 degrees, normal knees rolled back to -7.8 mm (range, -5.8 to -13.8 mm), but the mobile bearing total knee replaceme nt slid anteriorly to -5 mm (range, 2 to -12 mm), All mobile bearing t otal knee replacements had some form of roll back, but some slid anter ior more than others, Five of 10 mobile bearing total knee replacement s had some movement of the bearings while the others remained fixed, P atellar kinematics was similar to normal but reflected tibiofemoral ab normalities.