Thus, the data confirmed our hypothesis for rotations but not for translations. The loss of tibial screw-home was related to the symmetric femoral condyles, but the posterior translation in flexion was opposite the expected change after TKA with the PCL intact and the ACL excised. Thus, navigated TKA provided good coronal plane alignment but still lost some aspects of physiologic motion. The varus-valgus alignment and laxity did not change after TKA. There was a small tibial posterior translation from 40° to 90° flexion. The range of internal-external rotation was shifted externally from 30° to 20° extension. TKA caused loss of the screw-home the flexed tibia remained at the externally rotated position of normal full knee extension with considerably increased external rotation from 63° to 11° extension. The quadriceps was tensed and moments and drawer forces applied during knee flexion-extension while recording the kinematics with the navigation system. Using 8 cadaveric knees, we compared the kinematics of normal knees and TKA in a standardized navigated position with defined loads.
We hypothesized changes in rotations and translations after TKA with a fixed-bearing anterior cruciate ligament (ACL)-sacrificing but posterior cruciate ligament (PCL)-retaining design with equal-sized, circular femoral condyles would reflect the changes of articular geometry.
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