Although kinematic changes in the sagittal plane of the osteoarthritic knee (OA) have been elucidated, very few studies have analysed changes in the frontal and horizontal planes. Therefore, the aim of this study was to investigate in vivo 3D knee kinematics during walking in patients wth knee OA.
Thirty patients with medial knee OA and a control group of similarly aged individuals were prospectively collected for this study. All participants were assessed with KneeKG(TM) system while walking on a treadmill at a self-selected speed. In each trial, we calculated the angular displacment of flexion/extension, abduction/adduction and external/internal tibial rotation. Statistical analysis was performed to determine differences between the knee OA group and the control group.
Patients with knee OA had reduced extension during the stance phase (p < 0.05; 8.5° and 4.4°, OA and control group, respectively) and reduced flexion during pushoff and initial swing phase (p  < 0.05; 41.9° and 49.4°, respectively). Adduction angle was consistently greater for OA patients (p  < 0.05; 3.4° and -0.9°, respectively). Frontal laxity for OA patients was positively correlated with varus deformity (r = 0.42, p < 0.05). There was a significant difference (p)  < 0.05 in tibial rotation during the midstance phase; OA patients retained a neutral position (-0.4°), while the control group presented internal tibial rotation (-2.2°).
Weight-bearing kinematics in medial OA knees differs from that of normal knees. The knee OA group showed an altered "screw-home" mechanism by decreased excursion in sagittal and axial tibial rotation and posterior tibial translation.