Relationship Between Foot Kinematics and Center of Pressure Trajectory During Gait in Individuals with Flatfoot.

Background: Flatfoot causes the medial shift of ground reaction force during the stance phase of gait, which is associated with various foot disorders. To prevent this shift in flatfoot, it is necessary to understand the characteristics of the loading pattern and what foot joint kinematics influence it. We investigated differences in the center of pressure (COP) position between normal foot and flatfoot, and predictors of COP trajectory during gait.

Methods: Fifty healthy females participated. Based on the normalized navicular height truncated score, 27 and 23 participants were classified as having normal foot and flatfoot, respectively. Multisegmental foot kinematic and kinetic data were recorded during three gait trials. The COP trajectory was computed using a plantar local coordinate system defined from the obtained marker positions. COP positions during each phase of stance were compared between normal foot and flatfoot using independent t tests. Multiple regression analyses were performed to identify the relationship between foot joint motion and COP positions during each phase of stance.

Results: COP positions in flatfoot were displaced medially throughout the stance phase compared with normal foot. Multiple regression analyses revealed that the frontal and transversal plane motions of the calcaneus were main statistically significant predictors of the COP positions during the stance phase. Transversal plane motion of the calcaneus had greater standardized coefficients than in the frontal plane.

Conclusions: To correct the medial shift of the COP position in individuals with flatfoot, it may be important to control not only the eversion but also the adduction motion of the rearfoot throughout the stance phase.