Rotational and varus–valgus laxity affects kinematics of the normal knee: A cadaveric study

Purpose: The aim of this study was to evaluate the relationship between soft tissue laxity and kinematics of the normal knee using a navigation system. Methods: Fifteen cadaveric knees from 11 fresh frozen whole-body specimens were included in this study. The navigation system automatically recorded the rotation angle of the tibia as the internal–external (IE) kinematics and the coronal alignment of the lower limb as the varus–valgus (VV) kinematics. These measurements were made with the joint in maximal extension, at 10° intervals from 0° to 120° of flexion, and at maximal flexion during passive knee motion. For evaluation of laxity, the examiner gently applied maximum manual IE and VV stress to the knee at 0°, 30°, 60°, and 90° of flexion. Results: The measurements showed almost perfect reliability. The mean correlation coefficient between the intraoperative tibial rotation angle and the intermediate angle of IE laxity was 0.82, while that between the coronal alignment of the lower limb and the intermediate angle of the VV laxity was 0.96. There was a statistically significant correlation between kinematics and laxity at all degrees of knee flexion. Conclusion: The present study revealed that the rotation angle of the tibia was correlated to the intermediate angle of IE laxity at 0°, 30°, 60°, and 90° of knee flexion and the coronal alignment of the lower limb also correlated to the intermediate angle of VV laxity. These findings provide important reference data on soft tissue laxity and kinematics of the normal knee.