Determining the individual relationship between the step width and peak knee adduction moment during stepping in medial knee osteoarthritis

Background: Step-width modification can reduce peak knee adduction moment during gait in individuals with knee osteoarthritis, but determining optimal subject-specific step-width without testing multiple discrete positions remains a clinical challenge. Method: We investigated step-width's relationship with peak knee adduction moment in 14 individuals with medial knee osteoarthritis and 14 healthy controls using a robotic stepping system with motorized footplates moving between narrow, neutral, and wide step-widths. We analyzed peak knee adduction moment-step width relationship slopes and compared peak three-dimensional knee moments between all stepping conditions using repeated-measure ANOVA analysis. Findings: Both groups showed negative peak knee adduction moment-step width slopes, indicating reduced peak knee adduction moment with wider step-widths (knee osteoarthritis: P = 0.019, Controls: P = 0.016), with knee osteoarthritis group showing significantly higher slope and intercept values (P < 0.01, P < 0.001). Both groups demonstrated lower peak knee adduction moment and knee adduction moment impulse with wide step-width versus narrow and neutral step-widths (all P < 0.001). Lower peak knee adduction moment during wide step-width significantly correlated with increased tibia medial tilt (P < 0.001), increased footplate lateral reaction force (P = 0.023), reduced footplate inversion reaction torque (P < 0.001), reduced stepping speed (P = 0.022), and absence of knee osteoarthritis (P < 0.001). Interpretation: Wider step-width effectively reduces peak knee adduction moment and knee adduction moment impulse during stepping. The robotic stepping system enables precise subject-specific step-width determination using peak knee adduction moment-step width relationships, potentially offering individualized rehabilitation strategies for knee osteoarthritis management.