The Impact of Increased Knee Joint Flexion Angle During Loading Response on Mechanical Load of the Knee Joint in Healthy Elderly Individuals: A Cross-Sectional Study

Background and Objectives: According to the well-established correlation between knee joint contact force and external knee adduction moment (KAM) during walking, many studies have focused on gait modifications that target changes in the frontal plane, such as foot progression and trunk inclination angles, to decrease KAM. However, recent research has highlighted the relationship between the external knee flexion moment (KFM) and knee joint contact force, highlighting the importance of considering both the KAM and KFM in gait modifications that highlight changes in the sagittal plane. Consequently, the current study aimed to investigate the effects of increasing knee joint flexion angle while walking on knee joint loading. Methods: This study was a cross-sectional study. 20 healthy older adults each performed two gait conditions - normal walking and walking with a 10-degree increase in the maximum flexion angle, with five trials conducted for each condition. Results: The results showed that increasing the flexion angle significantly reduced KAM. Specifically, the first peak KAM decreased from 0.59 ± 0.24 to 0.43 ± 0.26 N·m/kg·m (p < 0.001), and the second peak KAM from 0.57 ± 0.20 to 0.45 ± 0.25 N·m/kg·m (p = 0.002). Conversely, the peak KFM increased significantly from 1.5 ± 0.48 to 1.8 ± 0.51 N·m/kg·m (p < 0.001). Furthermore, gait modification involved a straightforward intervention-merely providing verbal instructions to slightly increase knee flexion angle-making it both feasible and practical for older adults at higher risk of developing osteoarthritis of the knee (knee OA). Conclusions: Ensuring sufficient knee joint flexion angle during the early stance phase may serve as an effective instructional strategy for reducing KAM. Given its simplicity and non-invasive nature, this intervention may have practical potential for use in clinical or community-based gait training programs for older adults at risk of knee OA. However, these findings should be interpreted with caution when generalized to patients with knee OA. Such individuals may have altered muscle activation, increased joint sensitivity, or limited range of motion, which could affect their response to gait modification. Future studies involving longitudinal follow-up or patient-centered outcomes such as pain, function, and adherence will be necessary to evaluate the long-term clinical applicability of this intervention.