Peter A. Keblish

In vivo kinematic analysis of a mobile bearing total knee prosthesis.

Ten normal subjects and 10 patients with a posterior cruciate retaining 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) anterior, and -4.4 mm (range, 3.9 to 11 mm) posterior to the sagittal tibial midplane, respectively. At 60 degrees flexion, the normal knee rolled back to -5.8 mm (range, -2.5 to -13.2 mm), whereas the mobile bearing 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 replacement slid anteriorly to -5 mm (range, 2 to -12 mm). All mobile bearing total knee replacements had some form of roll back, but some slid anterior more than others. Five of 10 mobile bearing total knee replacements had some movement of the bearings while the others remained fixed. Patellar kinematics was similar to normal but reflected tibiofemoral abnormalities.

In-vivo kinematic analysis of a mobile bearing total knee prosthesis

Ten normal and ten patients with a posterior cruciate retaining meniscal hearing (having two articulating surfaces) TKA performed successive deep knee bends under fluoroscopic surveillance to determine the femorotibial contact positions. The purpose of this study was to analyze the kinematics of the meniscal bearing knee implant under in vivo, weightbearing conditions and to compare the obtained results to the kinematics of the normal knee. The fluoroscopic videos were analyzed using two techniques: (1) digitization and (2) image matching. For reference, a positive position is denoted as anterior and a negative position posterior to the midltne of the tibia. Total knee patients selected, had an excellent dinieal result (Avg. 96.0 New Jersey Knee Score) and had an average follow-up of 54 months. In contrast to normal knees, the femorotibial contact position for the meniseal bearing knee was posterior in full extension, similar to other posterior cruciate retaining designs analyzed using fluoroscopy. At full extension the average initial contact position for the normal and meniscal bearing knee groups was 6.2 (4.8 to 12.0ram), and 4.4 (3.9 to ll.Omm), respectively, ta 60 degrees of knee flexion, the average of the normal knee group rolled back to -5.8 (-2.5 to 13.2mm) and the meniseal hearing group roiled back to -9.2 (-4.0 to 17.0ram). From 60 to 90 degrees, the normal knee group continued to roll back to -7.8 m m (~5.8 to 13.8), but the meniscal bearing group slid in the anterior direction to an average position of -5.0mm (2.0 to 12.0). The normal knee group demonstrated a similar pattern for all subjects, but the meniscal bearing group demonstrated highly variable patterns. All meniscal bearing subjects demonstrated some form of roll back, but some slid anterior more than others. Five of the ten meniscal bearing knees demonstrated movement of the bearings during knee flexion, but the other five meniscaI heating knees had bearings that remained stationary during flexion. On average the meniscal bearing implant demonstrated femorotibial rollback from 0 to 60 degrees of knee flexion, but slid anterior from 60 to 90 degrees of flexion. The meniscal bearing implant is designed to slide in the A/P direction which may account for less wear at the femorotibial interface if the bearing motion occurs.

LCS® Multicenter Worldwide Outcome Study

Mobile bearings were originally introduced with the Oxford knee in 1977 which sought to improve articular congruity for improved wear characteristics using a spherical, congruous articulation while diminishing implant constraint with a floating surface p[6]. The Low Contact Stress (LCS) knee prosthesis (Depuy, Warsaw), the subject of this outcome study was a mobile bearing design with modifications of the tibial component to allow for posterior cruciate retention (meniscal bearing) or sacrifice (rotating platform). From the outset, it was recognized that a long term experience would be needed to prove the experiment that mobile bearings would solve the issues of fixation and wear through a favorable, high area of contact, wear surface and nonconstrained moveable bearings [2].