An evaluation of the velocity of the lateral thrust in osteoarthritic knees with a varus deformity

Lateral thrust of the knee on weight-bearing is seen frequently in patients with medial compartmental osteoarthritis (OA) of the knee while walking. The angular velocity of this abnormal lateral knee motion was calculated from the absolute angle of two vectors between co-instant points of three markers (anterior superior iliac spine, tibial tuberosity, and lateral malleolus) at heel contact and foot flat and the elapsed time in 46 medial compartmental osteoarthritic knees of 28 patients walking on a treadmill at a speed of 30 m/min. The osteoarthritic knees in this series were classified into two groups by abnormal findings in one leg standing radiograms; 31 knees in Group A with narrowing of the medial joint space and 15 knees in Group B with wear defect of the medial tibial plateau. The mean femoro-tibial angle and angular velocity of knee thrust in Group B (191.1±10.1°; 11.1° varus angulation, 51.6±18.6°/s) were higher than those in Group A (184.0±4.8°; 4° varus, 38.6±15.3°/s, respectively). The Hospital for Special Surgery (HSS) knee score in Group A (69.3±13.7 points) was higher than that in Group B (57.1±12.0 points). The angular velocity of knee thrust tended to be greater in knees with lower HSS score. The coefficient of correlation between the angular velocity of knee thrust and HSS score was −0.438 (P<0.01). A higher angular velocity of knee thrust was found in knees with more advanced medial compartmental osteoarthritis.