The purposes of this study were to understand the kinematics changes in the frontal and horizontal planes with severe medial knee OA at the stance phase and to examine the relationship between varus and rotational movements.
The OA group comprised 18 knees in 12 subjects (five men, seven women) with a Kellgren-Lawrence grade of three or four in at least one knee. From the results of gait analysis, we calculated Spearman rank-correlation coefficients for the following items: varus angle at initial contact (IC); varus angle at loading response (LR); amount of varus thrust from IC to LR; rotational angle at IC; rotational angle at LR and amount of rotational angle change from IC to LR.
The results indicated that, as the external rotation angle at IC and internal rotational movement from IC to LR increased, the maximum varus angle to LR showed a tendency to become large. In addition, varus thrust showed a tendency to become larger as the external rotation angles increased at IC and LR. The subjects with severe knee OA showed a strong correlation between the knee varus angle at IC and at LR. Furthermore, an increase in movement to internal rotation of the knee during the initial stance phase increased the knee varus angle at LR.
The control of the rotational movement according to the extent of varus thrust during the initial stance phase may have possible effects to decrease the load on the medial compartment of the knee.