Mechanical actions of individual muscles at the knee joint with varus/valgus malalignment

The mechanical actions of individual muscles crossing the knee joint were studied in the frontal plane. Through electrical stimulation, individual knee muscles were selectively activated and the resulting three-dimensional torques at the joint were measured. The isometric experiment was repeated at neutral, 5° varus, 5° valgus positions in the frontal plane and full knee extension to examine the effect of varus/valgus alignment on the muscle actions. In all muscles studied, the varus and valgus malalignment caused the muscles to exert a considerably larger torque in the direction opposite to that of the malalignment