Abstract
BACKGROUND: Persons with knee osteoarthritis demonstrate a reduction in knee joint excursion during loading response which is often coupled with a reduction in the moment acting to flex the knee. While these individual kinetic and kinematic changes are well documented, the interaction between changes in joint moment and changes in joint angle (dynamic joint stiffness) is not well understood in persons with knee osteoarthritis. METHODS: Twelve persons with severe knee osteoarthritis (Kellgren-Lawrence score 4) and 22 persons with moderate knee osteoarthritis (Kellgren-Lawrence scores 2-3) were compared to a healthy control group (n=22). Dynamic knee joint stiffness was calculated during loading response and was defined as the slope of the linear regression when joint moment is plotted against joint angle. Group differences were compared at 1.0m/s, self-selected and fast walking speeds using a one-way ANOVA, as well as a one-way ANCOVA to account for differences in freely chosen walking speed. Differences between speeds were compared using an ANOVA with one repeated measure (walking speed). FINDINGS: At all walking speeds, the severe group had significantly higher stiffness, even when accounting for differences in walking speed (P0.038). A significant increase in dynamic joint stiffness was found for all groups when speed was increased (P=0.001). INTERPRETATION: Persons with advanced stages of knee osteoarthritis develop higher joint stiffness irrespective of walking speed. While this may be a strategy to overcome knee instability often reported in this population during walking, the potential detrimental effects of higher dynamic joint stiffness should be explored in future research.