Impact of Knee Injury and Disease on Varus Thrust During Stair Descent on Different Surfaces

Quick lateral knee movement or rapid “bowing” during the weight acceptance phase of gait may characterize knee osteoarthritis development and progression. Yet, it is unknown whether it is impacted by different surfaces. This study investigated whether knee adduction biomechanics were impacted by surface during stair descent for individuals with knee injury (ACL Reconstruction: ACL-R) and disease (OA). Eighteen participants [4 control, 9 ACL-R, 5 OA] had knee adduction quantified when descending stairs with flat and uneven surfaces. Knee adduction biomechanics; including joint angular magnitude and velocity, jerk, varus thrust, and joint moment magnitude and velocity were submitted to a mixed model ANOVA. Contrary to our hypothesis, participants actually decreased varus thrust (p < 0.001), velocity of knee adduction joint angle (p < 0.001) and joint moment (p=0.012) on the uneven compared to flat surface. There was a surface by group interaction for normalized knee adduction jerk (p=0.035), where (ACL-R) participants exhibited “jerkier” knee adduction on the uneven surface (p=0.027). Participants adopted more cautious knee biomechanics, i.e., smaller, slower knee adduction when descending stairs with an uneven surface. However, further study is needed to determine whether caution was adopted to protect the knee or decrease fall risk.