The effect of total knee replacement on the knee varus angle and moment during walking and stair ascent

Background This study examined the effect of total knee replacement surgery on the frontal plane knee varus angle and moment. Secondarily, the relationships between knee varus angle and moment to a clinical outcome measure were assessed. Methods Twenty-one patients with total knee replacement and 21 controls performed level walking and stair ascent at two testing periods, pre- and 6-months post-surgery. The dependent variables included frontal plane knee angle and moment, and Western Ontario and McMaster Universities Osteoarthritis Index scores. Findings During level walking the mean knee varus moment of the patient group was significantly greater than controls at pre-surgery but was restored to control level post-operatively. During stair ascent the patient group produced a significantly smaller knee varus moment post-surgically. The mean frontal knee valgus angle of total knee replacement patients increased significantly from pre- to post-surgery during level walking. The Western Ontario and McMaster Universities Osteoarthritis Index score was not significantly correlated to the knee variables. However, the knee angle and moment were significantly correlated during level walking pre- and post-operatively and stair ascent post-operatively. Interpretation The decreased frontal plane knee moment in total knee replacement patients during level walking appeared to be affected by surgical realignment of the tibio–femoral joint, as the frontal knee angle and varus moment were strongly correlated. The subjective Western Ontario and McMaster Universities Osteoarthritis Index and the objective gait measures appeared to capture different dimensions of knee osteoarthritis.