BACKGROUND: Knee osteoarthritis (KOA) is a prevalent musculoskeletal disease affecting joint mechanics. Considering the effect of step-width changes on the biomechanics of gait, especially the alteration of stability dynamics during narrow-base gait, this study investigated the kinematic parameters of the lower extremities during both normal and narrow-base walking in individuals with and without KOA. METHODS: A cross-sectional study with 20 individuals with bilateral KOA and 20 controls was conducted. Participants walked on a treadmill at a preferred speed across normal and narrow paths. Joint angles and angular velocities in the sagittal and frontal planes were recorded, and mixed ANOVA was used to analyze group × condition effects. RESULTS: Significant main effects of walking condition were observed for hip (p = 0.001) and ankle angles (p = 0.002) in the frontal plane, and knee (p = 0.004) and ankle angular velocities (p = 0.002) in the sagittal plane. Moreover, there were significant main effects of group on the hip (p = 0.01) and knee angles (p = 0.04) in the sagittal plane. KOA group showed higher peak hip adduction (p <
0.001) and ankle inversion (p = 0.02]) during narrow-base walking than on the normal path. People with KOA had also significantly higher peak angular velocity of knee flexion (p = 0.03), ankle dorsiflexion (p = 0.002), and ankle inversion (p = 0.03) during narrow-base walking. CONCLUSIONS: The findings suggest that KOA and narrow-base gait challenges may trigger distinct kinematic adaptation strategies, potentially contributing to cartilage degeneration and altering balance mechanisms.