New Findings in Six-degrees-of-freedom Kinematics during Stationary Stepping in Patients with Knee Osteoarthritis

Background: Frontal plane knee kinematics are more likely associated with the development or progression of knee osteoarthritis. However, detailed frontal plane knee kinematics remain unclear. Previous studies examined movement during gait, squatting or stair stepping which allowed compensatory motion. However, biomechanical parameters in gait analyses can be modified. Therefore, we analyzed movement during stationary stepping activity while holding a handrail. The purpose was to determine: 1) detailed 6-degrees-of-freedom kinematics during stationary stepping activity in subjects with severe knee osteoarthritis; and 2) the association between unloading and black-loading phases. Methods: Twenty-four patients (32 knees) with severe medial knee osteoarthritis awaiting total knee arthroplasty were enrolled in this study. Knee kinematics was analyzed using a 3D-to-2D registration technique. Results: Knee adduction motion and tibial lateral translation increased from the unloading to weight-loading phase (P=0.027, P<0.001), but tibial internal-rotation motion was not increased (P=0.204). Knee adduction motion and tibial lateral translation motion were significantly correlated (r=0.400, P=0.023). Knee flexion angle during the weight-loading phase was negatively correlated with tibial lateral translation motion (r=0.597, P<0.001). Conclusions: A few studies that demonstrated detailed frontal plane knee kinematics have focused on the femoro-tibial motion. Severe knee osteoarthritis induced a greater knee adduction angle during the unloading phase, but the angle showed a smaller increase than that previously reported. Tibial lateral translation also increased during stationary stepping activity. Further work is needed to determine the association between femoro-tibial motion and varus thrust, and the association between knee flexion angle and intra-joint kinematics such as contact points. Level of Evidence: Cross-sectional study Level III