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This study investigated the relationships of pre- to postoperative changes in posterior condylar offset（PCO）to differences in condylar length and range of motion in posterior stabilized（PS）-type total knee arthroplasty（TKA）. Subjects and Methods: We studied 40 knees of 40 patients（10 males and 30 females）treated by PS-type TKA. Slide calipers were used to measure condyle lengths intraoperatively and PCO was measured by standard X-ray. The patients were divided into two groups based on a pre- to postoperative change in PCO of ≥ 3mm or＜3mm, with the differences in both condylar length and range of motion compared between groups. The mean differences in condyle lengths were 2.6mm（33 knees）and 4.3mm（7 knees）in cases with PCO changes of＜3mm and ≥ 3mm, respectively. The means in the respective groups were −6° and −7° for preoperative extension, 116° and 118° for preoperative flexion, −3° and −4° for postoperative extension, and 131° and 129° for postoperative flexion. There was no significant difference in the range of motion between the groups. Cases with a large difference in condylar lengths were likely to have a small PCO postoperatively; however, the postoperative range of knee flexion was not significantly related to a small postoperative PCO. These findings suggested that preoperative range of knee motion, age, and type of TKA could influence both the postoperative range of motion and PCO.

Different total knee arthroplasty （TKA） designs showed different intra-operative kinematics when evaluated with a navigation system. This study compared the kinematics of three different prosthesis designs using navigation-based in vivo simulation. Studies were carried out on 18 osteoarthritic knees using a computed tomography （CT）-free navigation system. The TKA designs used for these patients were six each of cruciate-retaining （CR） type, posterior-stabilized （PS） type, and PS mobile type. Intraoperative knee kinematics were measured during a passive range of motion from full extension to 130 degrees of knee flexion. Three types of prosthesis were compared for the following factors: the presence of condylar lift-off （gap difference greater than 1mm between medial gap and lateral gap） and anterior-posterior （AP） displacement of the center of femur relative to the tibia. The lift-off was found in patients with the PS type between 120° and 130° of flexion, but not in the other two types of implant. The pattern of AP displacement was similar among the three implants. The femur moved to the anterior side from extension to 50-55° of flexion, after that, the femur moved to the posterior side to full flexion. The function of PCL could prevent lift-off in the CR type of implants. In the PS-mobile implants, the mechanism of rotation platform might have contributed to lift-off prevention. The paradoxical anterior slide of the femoral condyles during mid flexion was observed in all types of implant.