A Technique for Assessing Foot Kinematics and Plantar Surface Characteristics During Stance for Varying Arch Structures

Clinical knowledge provides a framework for assessing the influence of the foot's arch structure on foot kinematics and plantar surface properties. However, attempts to quantify this relationship have resulted in conflicting outcomes and rely on inconsistent methodology. In this work, a technique was developed to examine foot mechanics and plantar surface characteristics during the stance phase of gait in individuals with different arch structures. Twenty-one subjects were categorized by arch height and flexibility and walked over a pressure mat while motion capture technology detected reflective markers placed on their feet. The trajectory data were used to analyze foot kinematics and calculate the relative deformation of the plantar surface in the vertical direction during walking. The force data were coupled with vertical position data to generate load-deformation curves of the plantar surface that depict the compression and relaxation of the plantar surface. The curves examine the changing stiffness during stance, the overall stiffness and dampening coefficients, and energy dissipation percentages. A generalized standard linear model was used to analyze statistical differences (p<0.05) with body mass index as a random effect parameter. The kinematic results showed statistical differences in mean and range between varying arch heights in the coronal tibia-heel rotations during the loading response and pre-swing, and the transverse plane during midstance and terminal stance. Arch flexibility statistically affected the coronal plane of the heel-tibia rotations during the loading response and midstance, and first metatarsal-midfoot rotations during terminal stance. The plantar surface characteristics showed statistical differences between varying arch heights in the stiffness and dampening properties under the fifth metatarsal, dampening of the midfoot, and energy dissipation ratio of the first metatarsal. There were statistical differences between varying arch flexibility structures in dampening of the midfoot and fifth metatarsal. Our results support kinematic differences in foot motion due to the arch structure, and the utility of combined plantar forces and kinematic data to depict load-deformation curves to detect differences in foot function during gait in varying arch structures. Overall, this technique assesses structural components of the plantar surface and functional mechanisms of foot motion to provide advancement in foot biomechanics research.