Knee Flexion Excursion Mediates the Association Between Quadriceps Stiffness and Knee Loads During the Mid-Stance Phase of Gait.

Lower strength and higher passive stiffness of the quadriceps have been associated with a higher risk of knee osteoarthritis/pain in aging populations. It is proposed that altered quadriceps properties would cause excessive knee loads, thus contributing to knee mechanical damages, but the relevant evidence is limited. This study aimed to explore relationships amongst quadriceps properties, knee flexions, and knee moments during gait. This study included 87 community-dwelling elders (65.9 ± 4.1 years; 57.5% females). Quadriceps strength was assessed using a Cybex dynamometer, and the passive stiffness of three superficial quadriceps heads was evaluated using shear-wave ultrasound elastography. Gait analysis was conducted to compute the knee adduction moment (KAM), knee flexion moment (KFM), KAM index, and knee flexion excursion (KFE) during the mid-stance phase. Associations amongst quadriceps properties, KFE, and knee moments were examined by partial correlations. Mediation analysis was used to explore the mediating role of KFE in associations between quadriceps properties and knee moments. Greater quadriceps strength was associated with a higher KAM (r = 0.304; p = 0.006). Greater stiffness of the rectus femoris (RF) was indirectly associated with a higher KAM index (mediation-effect [95% CI]: 0.084 [0.011, 0.191], p = 0.017) but a lower KFM (mediation-effect [95% CI]: -0.139 [-0.270, -0.041], p = 0.004), via a smaller KFE. Stronger quadriceps are correlated with a higher frontal knee moment. Stiffer RF is indirectly associated with a higher frontal knee load sharing through reduced sagittal knee motions, which could be a potential mechanism of stiffer RF for knee osteoarthritis.