Foot Progression Angle Modulates Knee Loading During Walking in Individuals with Flexible Flatfoot.

Abstract

This study evaluated tibiofemoral loading and medial meniscal stress distribution in individuals with flexible flatfoot (FFF) during walking under different foot progression angle (FPA) conditions. This study analyzed the gait of 28 FFF patients (16 males, 12 females) under three FPA conditions (neutral, toe-in, toe-out). Kinematic (Vicon) and kinetic (Kistler) data were used to estimate tibiofemoral forces in OpenSim. Subsequently, joint angles and muscle forces at peak tibiofemoral forces were used to drive a finite element (FE) model of the knee, enabling the comparison of meniscal von Mises stress, maximum shear stress, and contact pressure across FPA conditions. Tibiofemoral force increased during early stance (9-11%) in the toe-in condition with this increase reaching statistical significance in males (p = 0.008, mean partial <math xmlns="http://www.w3.org/1998/Math/MathML"> <mrow><msup><mi>η</mi> <mn>2</mn></msup> <mspace></mspace> <mo>=</mo> <mspace></mspace> <mn>0.70</mn></mrow> </math> within the SPM-identified cluster). FE analysis showed that peak stresses and contact pressure were primarily localized in the anterior region of the medial meniscus. A consistent directional response to FPA was observed with the lowest peak values occurring in the toe-in condition and the highest values in the toe-out condition. Adjusting FPA modulates intra-articular knee loading via the kinetic chain. For FFF patients, neutral FPA provides stable loading. The toe-in condition presents a complex mechanism: despite increasing tibiofemoral force (notably in males), it reduces peak stress by altering contact mechanics and stress distribution. Therefore, FFF gait interventions must be individualized based on factors like foot morphology, sex, and functional goals.